New in this version: Prince not involved

Updated at 7:30 p.m. ET: Two U.S. members of the NATO force in Southern Afghanistan were killed and several others were wounded Friday night in a complex attack on the U.S. Marine half of Camp Bastion/Leatherneck — the same camp where Britain's Prince Harry is based — U.S. and NATO officials told NBC News.

NATO officials said that Prince Harry was on the base at the time, but "never in any danger," Reuters reported.

AP file

Prince Harry at Camp Bastion/Leatherneck in Afghanistan last weekend. Initial reports were that he wasn't involved in the fighting that killed two U.S. members of the NATO force stationed there.

All of the casualties appeared to be Americans, NATO officials said.

The Leatherneck half of the joint NATO operations center in Helmand Province is home to members of the First Marine Expeditionary Force, which serves as the southwest regional command.

The attack, involving small arms and mortars, was launched against the International Security Assistance Force shortly after midnight local time (3 p.m. ET). Casualty assessments were still under way, but Camp Leatherneck took the brunt of the attack, officials said.

British defense officials told reporters only that they were "aware of an incident" at the base and that "the incident is being dealt with."

The Taliban launched what it called the "Harry Operations" on Monday, threatening to do everything in its power to kill Prince Harry, 27, who is third in line to the British throne, after British forces announced his four-month deployment to Camp Bastion.

Apart from the significance of the prince's being based there, the attack is notable as the worst yet on Camp Bastion/Leatherneck.

In March, a civilian Afghan worker tried to assassinate U.S. Defense Secretary Leon Panetta by driving his car into Panetta's plane as it arrived at the camp. The assailant died from burns; a British serviceman was injured.

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Syrian forces shelled opposition strongholds in the central province of Homs and eastern Deir al-Zor on Monday and clashed with rebels in violence that killed 29 people across the country, the Syrian Observatory for Human Rights said.

Activists said Syrian troops attacked a rebel-held town with helicopter gunships and shelled other restive areas across the nation. The aerial assault targeted the strategic river crossing town of Rastan, which has resisted repeated government offensives for months, the activists said. 

"The regime is now using helicopters more after its ground troops suffered major losses," said Rami Abdul-Rahman of the Britain-based anti-government group Syrian Observatory for Human Rights, which uses a network of sources on the ground. "Dozens of (military) vehicles have been destroyed or damaged" since the end of May, he said. 

'Battle is in Damascus' as Syrian tanks fire in 12-hour exchange

Syrian Foreign Ministry spokesman Jihad Makdissi recently said that rebels are now using sophisticated anti-tank missiles. Videos posted by activists over the past week have shown many destroyed tanks and armored personnel carriers. 

According to videos posted online, fireballs of orange flame and black rubble exploded in the air as waves of shells pounded residential buildings in Homs on Monday. The sounds of shells whooshed through the sky and there was occasional sporadic machine gun fire. 

The videos could not be independently verified. 

Annan: 'Gravely concerned'
Also on Monday, international envoy Kofi Annan said he was "gravely concerned" about the latest violence in the country, citing shelling of opposition areas of Homs and reports of mortar, helicopter and tank attacks near the coast. 

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In a statement, Annan said there was an escalation of fighting by government and opposition forces. Violence has spiked in recent weeks, with both sides ignoring a U.N.-brokered cease-fire that was supposed to go into effect on April 12 but never took hold. 

Annan demanded both sides "take all steps to ensure that civilians are not harmed." 

In Damascus, the state-run news agency SANA said authorities foiled an attempt to blow up a car rigged with 1,500 pounds of explosives in the Damascus suburb of Chebaa. Experts dismantled it Monday, SANA said. 

Syrian activists say 13,000 people have been killed in violence since the uprising began in March 2011. According to U.N. figures, soldiers and militias loyal to President Bashar Assad have killed at least 10,000 people.

Smell of death at the scene of massacre in Syrian village, UN monitors say

The bloodshed has led to broad condemnation of the regime from the international community, although Russia, Iran and China have stood by Assad. Russia and China have vetoed two Security Council resolutions that threatened sanctions against Syria. 

Russia has refused to support any move that could lead to foreign intervention in Syria, Moscow's last significant ally in the Middle East. 

Russian Foreign Minister Sergey Lavrov is scheduled to visit Syria's ally Iran on Wednesday.

The Associated Press and Reuters contributed this this report.

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