"Israeli authorities are increasingly practising state terrorism," the foreign ministry said in a statement carried by the official SANA news agency.
"The latest heinous Israeli aggression falls within the framework of ongoing Israeli attempts to prolong the crisis in Syria," it added.
Israeli airstrikes near Damascus and in Homs province late on Sunday killed nine mostly foreign pro-regime fighters and six civilians, including three children, the Britain-based Syrian Observatory for Human Rights said.
It was not immediately clear if the civilians died in the strikes or in their aftermath, it added.
An Israeli military spokeswoman declined to comment.
Syria's foreign ministry filed a complaint to the United Nations Security Council over the attack, demanding accountability, according to SANA.
It said Israel's "dangerous and hostile" actions would not have been possible without the support of its ally the United States, which protects it in the Security Council.
The strikes hit several Iranian positions near Damascus, and also targeted a research centre and a military airport west of the city of Homs where the Lebanese Shia movement Hizballah and Iranians are deployed, the Observatory said.
One of the pro-regime fighters killed was Syrian, while the rest were of other nationalities, Observatory chief Rami Abdel Rahman said.
Israel has carried out hundreds of air strikes in Syria since the beginning of the conflict in 2011, targeting forces loyal to President Bashar al-Assad and the regime's allies Iran and Hizballah.
The Syrian conflict has killed more than 370,000 people and drawn in world powers since it started in 2011 with the brutal repression of anti-government protests.
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