DUBAI -- Iran launched a submarine and a destroyer into the Persian Gulf from Bandar Abbas port on Tuesday at the same time as U.S. and allied forces held massive naval exercises in the same waters to practice keeping oil shipping lanes open.

Tehran has repeatedly threatened to close the Strait of Hormuz, a route for oil exports from the gulf, if Iranian nuclear sites are attacked by Israel, which believes Tehran is trying to develop an atomic bomb.

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The United States, Britain, France and a number of Middle Eastern states are conducting a naval exercise in the gulf this week, focusing on how to clear mines that Tehran or guerilla groups might deploy to disrupt tanker traffic.

The exercises, with 25 countries participating, are the largest ever of its kind in the region, according to Britain’s Telegraph newspaper 

The multinational force includes three U.S. Nimitz class carrier groups, each of which has more aircraft than Iran’s entire air force, the newspaper said.

The force is also supported by at least 12 battleships, including ballistic missile cruisers, frigates, destroyers and assault ships, which carry thousands of U.S. Marines and special forces, the Telegraph reported.

Netanyahu: Iran guided by 'unbelievable fanaticism'

Iran's refitted Tareq-901 submarine and Sahand destroyer were launched on the direct orders of Supreme Leader Ayatollah Ali Khamenei, the official IRNA news agency reported.

Iran's 'strong fence'
On the other side of the country, Khamenei visited the northern coastal city of Nowshahr on Tuesday to watch naval cadets practice planting mines, freeing hijacked ships, destroying enemy vessels and jumping from helicopters, his official website said.

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"The armed forces must reach capabilities such that no one can attack the strong fence of the country and the dear people of Iran," Khamenei told army commanders, according to the Iranian Students News Agency.

Iran's Tareq-class submarines are diesel-electric boats that were originally built in Russia in the early 1990s, according to the Nuclear Threat Initiative, a non-profit organization that focuses on security affairs.

Iran: 'Nothing will remain' of Israel if war starts

Israeli Prime Minister Benjamin Netanyahu said Sunday that Tehran was close to being able to build a nuclear bomb, fuelling speculation about an Israeli strike. Iran insists its nuclear program is peaceful.

Publicly, Iranian military officials have sounded relaxed about the U.S. naval exercise.

Complete Mideast & North Africa coverage on NBCNews.com

"This exercise is a defensive exercise and we don't perceive any threats from it," Mohammad Ali Jafari, commander of the Islamic Revolutionary Guard Corps, told local media.

"We are not conducting exercises in response," he said.

NBC News staff and Reuters contributed to this report.

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WASHINGTON – U.S. officials told NBC News on Tuesday that a small civilian boat was within 150 yards of a U.S. Navy ship in the Persian Gulf when it was fired upon, killing one and wounding three others on board.

The small skiff was heading straight for the USNS Rappahannock and ignored repeated warnings before the ship’s crew opened fire with a 50-caliber machine gun, officials said.

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The entire incident took place within a three-minute window about 10 miles offshore from Dubai, United Arab Emirates on Monday.

US vessel fires on boat in Gulf, killing one and injuring three

Pentagon officials on Tuesday released detailed timings of the incident, which began at 2:50 p.m. local time (5:50 a.m. ET). All times local.

2:50pm
The vessel, a motorized skiff, sighted at 5 miles, approaching Rappahannock from starboard (right) side at 20-25 knots.

2:51pm
The skiff now at 1200 yards when it turned inbound, headed directly for the Rappahannock

2:51pm
Rappahannock begins first phase of non-lethal warnings, radio, flashing lights. At 900 yards, the crew on the skiff ignores warnings and continues course directly at Rappahannock.

2:52pm
Now at 150 yards, skiff continues to ignore non-lethal warnings and continues course at Rappahannock.

2:52pm
As the skiff approaches 100 yards, the Rappahannock security team opens fire with a 50-caliber machine gun, killing one and wounding three others on board. The skiff slows for the first time, turns and circles around the stern and moves slowly up the port (left) side.

2:53pm
About 90 yards off the Rappahannock, the skiff comes to a stop.  Rappahannock goes to full speed to put distance between the two vessels.  The skiff is then seen departing the area.

It is unclear whether the dead and injured are from the United Arab Emirates or India, but U.S officials stress there is no indication that Iran or Iranians were in anyway involved.

The Pentagon also announced Monday that it is sending the aircraft carrier USS John C. Stennis to the Persian Gulf region – four months earlier than previously scheduled. The Stennis strike group, which also includes the Aegis guided-missile cruiser USS Mobile Bay and some 5,500 sailors, will also be on an eight month deployment – twice as long as the group was originally scheduled to be deployed.

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WASHINGTON – U.S. officials tell NBC News that at least one person was killed and three others injured when a U.S. Navy ship, the USNS Rappahannock, opened fire on a small boat about 10 miles offshore from Dubai in the Persian Gulf on Monday.

The U.S. officials say the boat, possibly a pleasure craft, ignored warnings and was closing in on the U.S. Navy supply ship in an "aggressive and threatening manner."

The crew aboard the Navy ship sent out repeated warnings, including radio calls, flashing lights, lasers and ultimately warning shots from a 50-caliber machine gun.  When the boat failed to heed the warnings, the crew was ordered to open fire with the 50-caliber gun.

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According to a press release from the Navy, “in accordance with Navy force protection procedures, the sailors on the USNS Rappahannock (T-AO 204) used a series of non-lethal, preplanned responses to warn the vessel before resorting to lethal force.”

U.S. officials say as of now it's unclear whether the dead and injured are from the United Arab Emirates or India, but they stress there is no indication that Iran or Iranians were in anyway involved in Monday's incident.

A U.S. Navy investigation is under way.

Iran: We can destroy US bases 'minutes after attack' 

Rising tensions
The Pentagon also announced Monday that it is sending the aircraft carrier USS John C. Stennis to the Persian Gulf region – four months earlier than previously scheduled. The Stennis strike group, which also includes the Aegis guided-missile cruiser USS Mobile Bay and some 5,500 sailors, will also be on an eight month deployment – twice as long as the group was originally scheduled to be deployed. 

This major shift in the Stennis deployment is a response to the steadily rising tensions over Iran's nuclear program, Iran's threat to shut down the Strait of Hormuz over tighter international sanctions, and the possibility that Israel may launch preemptive airstrikes against Iran's nuclear facility.

Full international coverage from NBCNews.com

The shift and extension of the Stennis deployment will allow CENTCOM to keep two aircraft carriers in the Persian Gulf region, Gulf of Oman and North Arabian Sea, not only as a hedge against Iran, but to support combat air operations over Afghanistan.

The aircraft Carrier USS Lincoln left the Persian Gulf area Monday.

Aircraft carrier USS Stennis going to Persian Gulf early, staying longer

The carriers Enterprise and Eisenhower will remain in the region until the Stennis relieves the Enterprise about five months from now.   

 Please check back in on this developing story. 

 NBC News' Jim Miklaszewski and Courtney Kube at the Pentagon, and The Associated Press contributed to this report.

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By Jim Miklaszewski, NBC News

US Navy officials report the aircraft carrier Abraham Lincoln and its battle group steamed through the Strait of Hormuz into the Persian Gulf Sunday without incident. It's the first US carrier to pass through the Strait since the Iranians threatened to attack the aircraft carrier Stennis three weeks ago, if it attempted to return to the Persian Gulf. Pentagon and US military officials have made it clear that Iranian threats would not deter the US Navy from operating in international waters in the Strait and the Gulf.

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US military officials say the Lincoln, with its guided-missile cruiser and two guided-missile destroyers, saw no sign of the Iranian navy speed boats which occasionally harass US warships as they pass through the Strait. Those incidents have increased, and in fact become somewhat routine since Iran's radical Revolutionary Guard has taken control of Iran's naval forces in the Strait and Persian Gulf.

Navy officials say the Lincoln battle group is in the Gulf on routine and regularly-scheduled exercises.

A second battle group led by the aircraft carrier USS Carl Vinson is in the Northern Arabian Sea conducting flight missions over Afghanistan.

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Casting aside current tensions between the U.S. and Iran, the U.S. Navy on Friday rescued 13 Iranian seamen who were being held captive by Somali pirates in the Gulf of Oman.

A Navy helicopter from the aircraft carrier USS John C. Stennis, responding to a distress call from a merchant ship under attack by pirates, chased the pirates to their "mother ship," an Iranian-flagged dhow that had earlier been hijacked.

 

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A heavily-armed counter-piracy team from the Navy destroyer USS Kidd met little resistance when they boarded the dhow where they found 15 armed pirates and the 13 Iranians who were being held hostage. The pirates were taken into custody. The Iranians were set free in their dhow.

 

The rescue occurred about 175 miles southeast of Muscat, Oman.

• STORY: Iran warns US carrier to stay out of Persian Gulf

It came less than two days after Iran threatened never to allow the USS John C. Stennis back to the Persian gulf following its departure last week for the Gulf of Oman and North Arabian Sea.

An Iranian surveillance plane last week video-recorded and photographed the vessel near the Strait of Hormuz, in a bid to cast its navy as having a powerful role in the region's waters.

• STORY: Iran tracks US aircraft carrier amid Strait of Hormuz tension

Iran has threatened to close the route in possible retaliation to new U.S. and European economic sanctions, a tactic the U.S. already has said it would not tolerate.

About one-sixth of the world's oil passes on tankers through the Strait of Hormuz, and analysts have warned the price of Brent crude could temporarily jump to as high as $210 if the strait is closed.

U.S. officials have said the Navy's Fifth Fleet, based in nearby Bahrain, is prepared to defend the shipping route.

White House officials said Iran's threat showed Tehran was increasingly isolated internationally, faced economic problems from to sanctions and wants to divert attention from its deepening problems.

"It reflects the fact that Iran is in a position of weakness," White House spokesman Jay Carney told reporters Tuesday.

• STORY: Iran oil standoff could mean higher gas prices

State news agency IRNA quoted Iranian army chief Ataollah Salehi as saying: "Iran will not repeat its warning ... the enemy's carrier has been moved to the Sea of Oman because of our drill. I recommend and emphasize to the American carrier not to return to the Persian Gulf.

"I advise, recommend and warn them (the Americans) over the return of this carrier to the Persian Gulf because we are not in the habit of warning more than once," he said.

• STORY: UK warns Iran over oil threat

Britain's defense secretary warned Iran Thursday that any attempt to block the key global oil passageway the Strait of Hormuz would be illegal and unsuccessful — hinting at a robust international response.

During his  first visit to the Pentagon for talks with U.S. Defense Secretary Leon Panetta, Philip Hammond told the Atlantic Council in Washington that the presence of British and American naval ships in the Persian Gulf would ensure the route is kept open for trade.

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  NBC's Jim Miklaszewski and msnbc.com staff contributed to this report.