Israel has rushed to beef up its rocket defences on its northern border to shield against possible retaliation after carrying out two airstrikes in Syria in the past 48 hours.

Syria and Iran hinted at possible retribution, though the rhetoric in official statements appeared relatively muted.

Despite new concerns about a regional war, Israeli officials signalled they will keep trying to block what they see as an effort by Iran to send sophisticated weapons to Lebanon's Hezbollah militia.

The moves are ahead of a possible collapse of Syrian President Bashar al-Assad's regime.

Israel has repeatedly threatened to intervene in the Syrian civil war.

It is trying to stop the transfer of what it calls "game-changing" weapons to Hezbollah.

Hezbollah is Syrian-backed group that battled Israel to a stalemate during a month long war in 2006.

Since carrying out a lone airstrike in January that reportedly destroyed a shipment of anti-aircraft missiles headed to Hezbollah, Israel had largely stayed on the sidelines.

That changed over the weekend with a pair of airstrikes.

The airstrikes included an attack near a sprawling military complex close to the Syrian capital of Damascus early yesterday that set off a series of powerful explosions.

The Israeli government and military refused to comment.

But a senior Israeli official said both airstrikes targeted shipments of Fateh-110 missiles bound for Hezbollah.

The Iranian-made guided missiles can fly deep into Israel and deliver powerful half-ton bombs with pinpoint accuracy.

The official spoke on condition of anonymity because he was discussing a covert military operation.

Syria's government called the attacks a "flagrant violation of international law" that has made the Middle East "more dangerous."

It also claimed the Israeli strikes proved the Jewish state's links to rebel groups trying to overthrow Assad's regime.

Syria's information minister, Omran al-Zoubi, reading a Cabinet statement after an emergency government meeting, said Syria has the right and duty "to defend its people by all available means."

Israeli defense officials believe Assad has little desire to open a new front with Israel when he is preoccupied with the survival of his regime.

More than 70,000 people have been killed since the uprising against Assad erupted in March 2011, and Israeli officials believe it is only a matter of time before Assad is toppled.

Meanwhile, the United Nations has said that chemical weapons have been used by the rebels in the Syrian conflict.

Assad's government and the rebels accuse each other of carrying out three chemical weapon attacks, one near Aleppo and another near Damascus, both in March, and another in Homs in December.