JERUSALEM -- Syria's allies on Thursday condemned an Israeli airstrike a day earlier on a Syrian target, with Iran making a veiled threat to respond. Israeli analysts said, however, that the likelihood of retaliatory attacks was slim.

As Israeli officials voiced rising concern earlier this week about the security of Syria's chemical weapons, the military moved missile-defense batteries to northern Israel and anxious Israelis lined up at some gas-mask distribution centers. But Israeli authorities took no extraordinary measures to prepare for a possible response after Wednesday's airstrike, apparently calculating that the turmoil in Syria and Israel's military deterrence would discourage any hostilities.

Details of the attack remained murky, and the United States and Israel maintained a public silence in what analysts said was probably a calculated decision to reduce the prospect of retaliation. Western officials and a former Lebanese security official initially said the strike was carried out near Syria's border with Lebanon and possibly hit a truck ferrying weapons to Hezbollah militants in Lebanon, but Syria later announced that a defense research center near Damascus had been bombed.

The statement from Syria prompted allies to spring to its defense Thursday. Iran's deputy foreign minister, Hossein Amir-Abdollahian, was quoted by Iranian news agencies as warning Israel of "grave consequences" after the airstrike.

Hinting at possible retaliation, Amir-Abdollahian said Israel should not rely on its Iron Dome missile shield, which he said proved ineffective during Israel's military offensive in November against the militant Hamas group in the Gaza Strip. The system stopped scores of incoming rockets, but others struck southern Israeli cities and reached areas near Jerusalem and Tel Aviv.

Clinton speaks out

Russia, Syria's most powerful ally, said in a statement that if the strike is confirmed, "we have a case of unprovoked attacks on targets in the territory of a sovereign state, which grossly violates the U.N. charter and is unacceptable.''

In Washington, outgoing Secretary of State Hillary Rodham Clinton declined to discuss the Israeli strike, but she said Iran and Russia were continuing -- and, in Iran's case, increasing -- their assistance to Syrian President Bashar Assad.

Clinton dismissed Russian Prime Minister Dmitry Medvedev's call this week for negotiations between Assad and his opponents. The Russians, she said in an exit interview with State Department correspondents, are not "passive bystanders in their support for Assad" and are continuing to send financial aid and military equipment to his government.

Iran, Clinton said, had expanded the number of fighters, trainers and supplies it is sending to the Syrian military. "We know that the Iranians are all in for Assad," she said.

Syria's ambassador to Lebanon, Ali Abdul Karim Ali, was quoted on Hezbollah's Al-Ahd news website as saying that Syria could launch a "surprise" retaliation, but he added that he could not predict when such a response might come. Hezbollah called the Israeli strike "savage aggression" and expressed "full solidarity with Syria's leadership, army and people," but it, too, did not threaten to retaliate.

Hezbollah, which defense analysts say has expanded its arsenal to include as many as 50,000 missiles, has avoided firing rockets across the border since a war with Israel in 2006 that devastated the group's strongholds in southern Lebanese villages and parts of Beirut.

'Total military disarray'

Despite the tough rhetoric from Syria and its allies, Israeli analysts said Syria's precarious position, which has also weakened Hezbollah, made retaliation unlikely.

"Syria is in total military disarray,'' said Itamar Rabinovich, a former Israeli ambassador to Washington who was Israel's chief negotiator with Syria in the 1990s. "The Syrian army can't cope with ragtag bands of rebels, so it's not up to taking on Israel.

"Hezbollah is in a delicate position in Lebanon, where it has been weakened by its unpopular support for the Syrian regime. Getting Lebanon in trouble again is not what they need."

Shlomo Brom, a senior research fellow at the Institute for National Security Studies in Tel Aviv, said Syria was not likely to risk further damage to its military through a confrontation with Israel. Hezbollah, he added, has similar concerns.

"If Hezbollah launches rockets at Israel, it will start a large conflict whose cost will be borne mostly by Lebanon and its citizens," Brom said. "The last thing they need is to be accused of causing the destruction of Lebanon."

Iran also has an interest in avoiding a military clash with Israel that could lead to strikes on its nuclear facilities, Rabinovich said. "They have other ways of striking back, encouraging terrorist activity here or around the globe."