A Syrian activist group says Israel's weekend airstrike on a sprawling military complex near the Syrian capital Damascus has killed at least 42 Syrian soldiers.

The Britain-based Syrian Observatory for Human Rights said Monday that the toll is based on information from sources in Syrian military hospitals.

The Syrian government has not released a death toll. Immediately after Sunday's predawn strike, Syrian state media said the attack caused casualties, but did not elaborate.

So far, Israel has carried out three airstrikes in Syria this year, according to Israeli and U.S. officials, though Israel's government has not formally confirmed involvement.

The officials say the attacks were meant to prevent advanced Iranian weapons from reaching Lebanon's Hezbollah militia, a Syria ally and Israel foe.