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.
Copyright 2013 The Associated Press.