ACTION

BEIRUT, Lebanon — A series of powerful explosions rocked the outskirts of Damascus early Sunday morning, which Syrian state television said was the result of Israeli missile attacks on a Syrian military installation.

If true, it would be the second Israeli airstrike in Syria in two days and the third this year.

The airstrike that Israeli warplanes carried out in Syria overnight on Thursday was directed at a shipment of advanced surface-to-surface missiles from Iran that Israel believed was intended for Hezbollah, American officials said Saturday. That strike was aimed at disrupting the arms pipeline that runs from Syria to Hezbollah, the militant Lebanese organization, and it highlighted the mounting stakes for Hezbollah and Israel as Syria becomes more chaotic.

Iran and Hezbollah have both backed President Bashar al-Assad in the Syrian civil war, now in its third year. But as fighting in Syria escalates, they also have a powerful interest in expediting the delivery of advanced weapons to Hezbollah in case Mr. Assad loses his grip on power and Syria ceases to be an effective channel for funneling weapons from Iran.

The missiles that were the target of the Israeli raid had been shipped from Iran and were being stored in a warehouse at Damascus International Airport when they were struck, according to an American official.

Iran has sought to use the threat of a Hezbollah missile attack against Israeli territory as a means of building up its ally and deterring Israel from conducting airstrikes on Iranian nuclear installations that Israeli and American officials believe are part of an Iranian nuclear weapons program.

In Lebanon, some analysts said they believed that a strong Hezbollah could also emerge as a powerful ally for Mr. Assad if he is forced to abandon Damascus, the Syrian capital, and take refuge in a rump Iranian-backed state on the Syrian coast, a region that abuts the Hezbollah-controlled northern Bekaa Valley.

“The relationship between Hezbollah and the Assad regime is stronger now,” said Talal Atrissi, a professor at Lebanese University in Beirut who has good relations with Hezbollah. If Mr. Assad falls, Hezbollah knows the axis of Syria, Hezbollah and Iran will be greatly weakened, he said.

Israel, for its part, has repeatedly cautioned that it will not allow Hezbollah to receive “game changing” weapons that could threaten the Israeli heartland even if a new Syrian government takes power.

As the Obama administration considers how to dissuade Mr. Assad from ordering a chemical weapons attack — the use of such weapons, the White House has said, would cross a “red line” — Israel, by striking the warehouse, is clearly showing that it is prepared to stand behind the red lines it has set.

“The Israelis are saying, ‘O.K., whichever way the civil war is going, we are going to keep our red lines, which are different from Obama’s,’ ” said Ehud Yaari, an Israel-based fellow of the Washington Institute for Near East Policy.

On Friday, SANA, the official Syrian news agency, reported an attack on the Damascus airport by Syrian rebels firing rockets at an aircraft and fuel dump — an account that American officials say may have been intended to obscure the fact that the target was a warehouse full of missiles.