Israel remained quiet Monday on reports it conducted air strikes on Syrian targets over the weekend, but U.S. officials said Israel had the right to destroy weapons it believes may be used in attacks on its soil.

Images on Syrian television showed unknown buildings hit by what Syria’s information minister said were Israeli missiles. Explosions rocked Damascus Sunday and reports from anti-government activists suggested that a military complex was among the buildings destroyed, a blast that killed 42 soldiers.

“The Israeli invaders committed a blatant act of aggression against Syria on Sunday morning,” said Syria’s information minister Omran al-Zoabi.

The strikes were the second such activity in three days, with U.S. intelligence officials reporting explosions at Syrian weapons facilities last Friday.

Israeli officials would not comment on the strikes. However, U.S. intelligence sources said Sunday’s attacks appeared to target missiles set to be handed over to Hezbollah, a Syrian ally, in Lebanon.

"The Syrians and Iranians have crossed a red line of the Israelis and that means that weapons of advanced nature, probably missiles, have been moved from Iran into Syria with intentions of moving them to Hezbollah,” U.S. Sen. John McCain said Sunday.

Meanwhile, in Ottawa, MPs will hold an emergency debate about the situation in Syria on Tuesday.

The Israeli army is on high alert in the Golan Heights, which is just across the border from Syria, and Israel’s missile defence system has been shifted northward toward Lebanon.

White House spokesperson Jay Carney told reporters Monday to ask Israeli officials about the strikes. However, he said Israel, “certainly has the right to be concerned about the transfer of sophisticated weapons to Hezbollah.”

Carney went on: “The transfer of sophisticated weapons to terrorist organizations like Hezbollah is certainly a concern and a threat to Israel, and they have the right to act in their own sovereign interest on ... in response to those concerns."

On Monday, Syrian and Iranian officials hinted at retaliatory strikes.

Iranian Foreign Minister Ali Akbar Salehi warned that Israel was "playing with fire" and suggested that groups such as Hezbollah could hit back. 

Carney also told reporters Monday that it is likely that the Syrian government led by President Bashar Assad and not the rebel opposition is responsible for any use of chemical weapons inside the country.

Carney disputed a claim by a UN official investigating the goings-on in Syria that rebels had used the nerve gas sarin against citizens.

"We are highly skeptical of suggestions that the opposition could have or did use chemical weapons," Carney said. "We find it highly likely that any chemical weapon use that has taken place in Syria was done by the Assad regime. And that remains our position."

Carney noted the Obama administration is still seeking conclusive evidence that chemical weapons have indeed been used in the country.

With a report from CTV’s Middle East Bureau Chief Martin Seemungal and files from The Associated Press