BEIRUT - Israeli missiles struck a research center near the Syrian capital Damascus, setting off explosions and causing casualties, Syria's state news agency reported early Sunday, citing initial reports.
If confirmed, it would be the second Israeli strike on targets in Syria in three days, signaling a sharp escalation of Israel's involvement in Syria's bloody civil war.
There was no immediate Israeli comment. However, Israel has said it will not allow sophisticated weapons to flow from Syria to the Lebanese Hezbollah militia, an ally of Syrian President Bashar Assad and a heavily armed foe of the Jewish state.
Two previous Israeli airstrikes, one in January and one on Friday, targeted weapons apparently bound for Hezbollah, Israeli and U.S. officials have said.
The Syrian state news agency SANA reported early Sunday that explosions went off at the Jamraya research center near Damascus, causing casualties. "Initial reports point to these explosions being a result of Israeli missiles that targeted the research center in Jamraya," SANA said.
A Syrian activist group, the Britain-based Syrian Observatory for Human Rights, also reported large explosions in the area of Jamraya, a military and scientific research facility northwest of Damascus, about 15 kilometers (10 miles) from the Lebanese border.
An amateur video said to be shot early Sunday in the Damascus area showed a huge ball of fire lighting up the night sky. The video appeared genuine and corresponded to other Associated Press reporting.
Israel's first airstrike in Syria, in January, also struck Jamraya.
At the time, a U.S. official said Israel targeted trucks next to the research center that carried SA-17 anti-aircraft missiles. The strikes hit both the trucks and the research facility, the official said. The Syrian military didn't confirm a hit on a weapons shipment at the time, saying only that Israeli warplanes bombed the research center.
On Saturday, Israeli officials confirmed that a day earlier, Israeli aircraft targeted advanced surface-to-surface missiles in Syria that were apparently bound for Hezbollah.
The missiles were believed to be m600s, a Syrian version of Iran's Fatah 110 missile, an extremely accurate guided missile capable of traveling roughly 300 kilometers (190 miles) with a half-ton warhead, an Israeli official said
The Israeli officials spoke anonymously because they had not been given permission to speak publicly about the matter.
In Washington, a Pentagon spokeswoman said she had no information relating to Sunday's report of a new Israeli airstrike in Syria.
President Barack Obama said Saturday, before the latest incident, that 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.
Israel has said it wants to stay out of the brutal Syria war, but could inadvertently be drawn in as it tries to bolster its deterrence and prevent sophisticated weapons from reaching Hezbollah.
Since the conflict in Syria erupted more than two years ago, fighting has repeatedly spilled into Turkey, Lebanon, Iraq, Jordan and the Israeli-annexed Golan Heights.
Renewed concern about a wider conflagration come as Washington considers how to respond to indications that the Syrian regime may have used chemical weapons in its civil war.
Obama has described the use of such weapons as a "red line," and the administration is weighing its options -- including possible military action.
Prime Minister Benjamin Netanyahu, meanwhile, has drawn his own red line, saying repeatedly that the Jewish state would be prepared to take military action to prevent Hezbollah from obtaining new weapons that could upset the balance of power.
Israel believes Hezbollah has restocked its arsenal with tens of thousands of rockets and missiles since a 2006 war between the two ended in a stalemate.
Israel is concerned that Hezbollah will take advantage of the chaos in Syria to smuggle advanced weapons into Lebanon.
These include anti-aircraft missiles, which could hamper Israel's ability to operate in Lebanese skies, and advanced Yakhont missiles that are used to attack naval ships from the coast.
In recent days, there were signs of mounting tensions between Israel and Hezbollah.
In a warning to Israel earlier this week, Hezbollah chief Hassan Nasrallah said his militia "is ready and has its hand on the trigger" in the event of an Israeli attack on any targets in Lebanon.
The Israeli military, meanwhile, called up several thousand reservists earlier this week for what it called a "surprise" military exercise on its border with Lebanon.
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