"Israeli warplanes targeted the Palmyra military airport," the Britain-based Syrian Observatory for Human Rights said.

Since Islamist-led rebels overthrew Assad in December, Israel has launched hundreds of strikes on military sites in Syria, saying it wants to prevent weapons from falling into the hands of the new authorities whom it considers jihadists.

The Syrian rebels included those who once formed Al-Qaeda's branch in Syria, though the new government has sought to distance itself from that past.

The Israeli military has also deployed to the UN-patrolled buffer zone on the Golan Heights, separating the Israeli-occupied part of the Golan from that still controlled by Syria.

Israeli Prime Minister Benjamin Netanyahu has demanded the demilitarisation of southern Syria and said his country will not tolerate the presence of forces from the new authorities south of the capital Damascus.

Syria's foreign ministry has accused Israel of waging a campaign against "the stability of the country".