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Israel strikes Syrian military research center, US official says

Syrian opposition forces got a boost from two nights of Israeli airstrikes against President Assad's regime, NBC's Richard Engel reports.

Israeli jets bombed a military research facility north of Damascus early Sunday, a senior official told NBC News. It marked the second Israeli attack on targets in Syria in recent days. 

Heavy explosions shook the city, and video shot by activists showed a fireball rising into the sky after Sunday's strikes.

Reuters reported that a Western intelligence source said the operation hit Iranian-supplied missiles that were en route to the Hezbollah militia in Lebanon.

A rebel spokesman, who spoke from a “liberated area” held by the opposition in Damascus, told NBC News there were huge explosions just before 2 a.m. Sunday local time (7 p.m. Saturday ET) in the Qaysoun mountains on the edge of Damascus. 

“Around 10 locations were hit," the spokesman said. "It was difficult to tell what was hit in the raid and what exploded afterwards.  Some of the targets were weapons and weapons depots.

"Secondary explosions continued for about four hours.  They shook all of Damascus. There was still smoke in the air as the sun came up.”

From its Damascus media office, the Free Syrian Army listed nine apparent targets, including the Syrian Revolutionary Guard, the 104th brigade headquarters, a weapons depot in Qasyoun and a military research center at Jamraya.

The FSA said power was cut in parts of Damascus at 1:48 am local time Sunday (6:48 p.m. Saturday ET). A FSA spokesman said the fires and explosions "made Damascus look like the day at night."

The White House said there would be no official comment on the latest attack, but diplomatic sources and U.S. officials told NBC News that the administration is fully supportive of the airstrikes.

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A look back at the conflict that has overtaken the country.

United Nations Secretary General Ban Ki-moon said he spoke with the head of the Arab League, Nabil ElAraby, about the Israeli air strikes on Sunday and expressed "grave concern" for the risks to regional security. 

On Friday, Israeli warplanes launched strikes against targets inside Syria, U.S. officials told NBC News. It’s believed the primary target also was a shipment of weapons headed for Hezbollah, they said. A senior U.S. official said the airstrikes were believed to be related to delivery systems for chemical weapons.

After that attack, an Israeli spokesman in Washington said that Israel would not comment specifically on the reports but said that “Israel is determined to prevent the transfer of chemical weapons or other game-changing weaponry by the Syrian regime to terrorists, especially to Hezbollah in Lebanon.”

It wasn’t clear whether the Israelis alerted the U.S. before the attack. White House officials referred all questions to the Israelis.

Rebel units were in disagreement about what type of weapons were in the convoy, Reuters reported. A rebel from an information-gathering unit in Damascus that calls itself "The Syrian Islamic Masts Intelligence" said the convoy carried anti-aircraft missiles.

The rebel, who asked not to be named, added: "There were three strikes by Israeli F-16 jets that damaged a convoy carrying anti-aircraft missiles heading to the Shi'ite Lebanese party (Hezbollah) along the Damascus-Beirut military road. One strike hit a site near the (Syrian) Fourth Armoured Division in al-Saboura but we have been unable to determine what is in that location."

However, Qassim Saadedine, a commander and spokesman for the rebel Free Syrian Army, told Reuters he did not think the weapons were anti-aircraft. "We have nothing confirmed yet but we are assuming that it is some type of long-range missile that would be capable of carrying chemical materials," he said. 

In the January attack, Israeli fighter jets struck a convoy of sophisticated anti-aircraft missiles believed on their way to Hezbollah.  

Israeli Defense Minister Moshe Ya’alon publicly acknowledged the January airstrike inside Syria in a joint press conference with Defense Secretary Chuck Hagel in Tel Aviv on April 22. Ya’alon said any Syrian delivery of sophisticated weapons to rogue elements like Hezbollah would be a “red line” for Israel and “when they crossed this red line, we operated. We acted.”

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Syria is in the middle of a civil war pitting rebels against the regime of President Bashir Assad. Tens of thousands have already died, and the possible use of the nation’s stockpile of chemical weapons has been of grave concern to the U.S. and other nations.

Last week, the White House said there was evidence that Syria’s government may have used chemical weapons against its own people. But President Barack Obama has cautioned against rushing to action against Assad’s government, saying that the U.S. required more evidence before getting involved in the civil war there.  

The U.S. has long believed that Syria was stockpiling chemical weapons. Intelligence reports indicate that it has sarin and the nerve agent tabun along with traditional chemicals like mustard gas and hydrogen cyanide. A 2011 CIA report said Syria was also developing the potent nerve agent VX, which could render a city uninhabitable for days.

Syria has said that it hasn’t used and will not use chemical weapons.

On Tuesday, Hezbollah’s leader warned the rebels that his militia was ready to intervene on Assad’s side in Syria’s civil war. There have been concerns that Syrian SCUD missiles that might be capable of carrying chemical weapons could be transferred to Hezbollah.

NBC News' Richard Engel, Kristen Welker and Stacey Klein and Reuters contributed to this report.

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