Syrian state TV is reporting that another Israeli airstrike has hit the country, this time targeting a military research center near Damascus.
A Syrian activist group, the Britain-based Syrian Observatory for Human Rights, reported large explosions in the area of the Jamraya research center early Sunday.
If confirmed, Sunday's strike would mark the third Israeli attack inside Syria this year. Israel has said it will not allow sophisticated weapons to flow from Syria to the Lebanese militia Hezbollah, an ally of the regime of Syrian President Bashar Assad.
Israeli officials were not immediately available for comment early Sunday.
On Saturday, Israeli officials confirmed that a day earlier Israeli aircraft targeted a weapons shipment apparently bound for Hezbollah.
The officials said the attack took place early Friday and was aimed at sophisticated "game-changing" weapons, but not chemical arms. One official said the target was a shipment of advanced, long-range ground-to-ground missiles but was not more specific.
It was not immediately clear where the attack took place, or whether the air force carried out the strike from Lebanese or Syrian airspace.
The Israeli officials spoke on condition of anonymity because they were not authorized to disclose information about a secret military operation to the media.
U.S. officials had earlier confirmed the airstrike but said only that it appeared to have hit a warehouse.
Calls to the Israeli military and defense ministry were not immediately answered.
Israeli Prime Minister Benjamin Netanyahu has repeatedly warned in recent weeks that Israel would be prepared to take military action if chemical weapons or other arms that would upset the balance of power with Hezbollah were to reach the Islamic militant group.
Syria's assistant information minister, Khalaf Muftah, told Hezbollah's Manar TV that he has "no information about an aggression that was staged," and said reports of an Israeli air raid "come in the framework of psychological war in preparation of an aggression against Syria."
It's not the first time since Syria's crisis erupted in March 2011 that Israel has intervened struck inside Syria.
In January, the Israeli air force is believed to have targeted a shipment of advanced SA-17 anti-aircraft missiles bound for Hezbollah. Israel has not formally admitted to carrying out that airstrike, though officials have strongly hinted they were behind the attack.
The airstrikes follow decades of enmity between Israel and allies Syria and Hezbollah, which consider the Jewish state their mortal enemy. The situation has been further complicated by the civil war raging in Syria between President Bashar Assad regime and rebel brigades seeking his ouster.
The war has drained Assad's military and threatens to deprive Hezbollah of a key supporter, in addition to its land corridor to Iran. The two countries provide Hezbollah with the bulk of its funding and arms.
Israel and Hezbollah fought an inconclusive 34-day war in 2006 that left 1,200 Lebanese and 160 Israelis dead.
While the border has been largely quiet since, the struggle has taken other forms. Hezbollah has accused Israel of assassinating a top commander, and Israel blamed Hezbollah and Iran for a July 2012 attack on Israeli tourists in Bulgaria. In October, Hezbollah launched an Iranian-made reconnaissance drone over Israel, using the incident to brag about its expanding capabilities.
Details about Friday's strike remained sketchy.
The U.S. officials said the airstrike apparently hit a warehouse, but gave no other details.
Israeli officials did not say where in Syria the Israeli aircraft struck or whether they fired from Lebanese, Syrian or Israeli airspace.
Israel possesses bombs that can travel a long distance before striking their target. The use of such weapons could allow Israel to carry out the attack without entering Syrian skies, which would risk coming under fire from the regime's advanced, Russian-made anti-aircraft defenses.
The Israeli and U.S. officials spoke anonymously because they had not been given permission to speak publicly about the matter.
Obama said Saturday that he wouldn't comment on the Israeli airstrike against Syria. He said it was up to Israel to confirm or deny any strikes, but that the U.S. coordinates very closely with Israel.
"The Israelis, justifiably, have to guard against the transfer of advanced weaponry to terrorist organizations like Hezbollah," Obama told the Spanish-language TV station Telemundo.
