Israel's weekend airstrike on a sprawling military complex near the Syrian capital killed at least 42 Syrian soldiers, an activist group has said.
The Britain-based Syrian Observatory for Human Rights said 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 pre-dawn strike, Syrian state media said the attack near Damascus caused casualties, but did not elaborate.
So far, Israel has carried out three airstrikes in Syria this year, according to Israeli and US 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.
Syria and its patron Iran have hinted at possible retribution over the strikes, though the rhetoric in official statements has been relatively muted.
Iranian Foreign Minister Ali Akbar Salehi warned that Israel was "playing with fire," but gave no other suggestions of possible consequences, according to the official Islamic Republic News Agency.
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 Israel's links to rebel groups trying to overthrow Syrian President Bashar Assad's regime..
Israeli officials have indicated they will keep trying to block what they see as an effort by Iran to send sophisticated weapons to Lebanon's Hezbollah militia ahead of a possible collapse of Assad's regime.
Israel has repeatedly threatened to intervene in the Syrian civil war to stop the transfer of what it calls "game-changing" weapons to Hezbollah, a Syrian-backed group that battled Israel to a stalemate during a month-long war in 2006.