The Israeli army confirmed it carried out deadly strikes on Syrian and Iranian targets near Damascus on Wednesday, in response to fire from Syria the day before.
The army, which blamed Tuesday's rockets on "an Iranian force", said it holds Damascus responsible for attacks launched from Syria into its territory.
Eleven "fighters", including seven foreigners, were killed in the strikes, the Syrian Observatory for Human Rights said.
"We cannot confirm whether the seven foreigners were all Iranian or pro-Iranian fighters of different nationalities," the head of the Britain-based group, Rami Abdel Rahman, told AFP.
Syria's state media earlier said Syrian anti-aircraft defenses intercepted a "heavy attack" by Israeli warplanes over the capital in the early hours of Wednesday morning.
"We just carried out wide-scale strikes of Iranian Quds Force & Syrian Armed Forces targets in Syria in response to the rockets fired at Israel by an Iranian force in Syria last night," the Israeli army tweeted.
During the attack the Syrian regime's defense missile was fired "despite clear warnings to refrain from such fire", it added. As a result, a number of Syrian aerial defense batteries were destroyed.
"We hold the Syrian regime responsible for the actions that take place in Syrian territory and warn them against allowing further attacks against Israel," the army said.
"We will continue operating firmly and for as long as necessary against the Iranian entrenchment in Syria."
Israel has carried out frequent air and missile strikes against Iranian targets inside Syria since the country descended into civil war in 2011, but rarely comments on them.
Wednesday's air raid comes a day after Israel's defenses intercepted four rockets fired from Syria.
The Syrian Observatory for Human Rights said Tuesday's rockets were fired from positions around the capital held by groups loyal to the Damascus regime.
The hundreds of strikes carried out by Israel in Syria have mostly been against Iranian targets or positions of Iran's Lebanese ally Hezbollah.
Russian Deputy Foreign Minister Mikhail Bogdanov said on Wednesday that Israeli air strikes on Syria were a wrong move, and Moscow had contacted its allies about the incident, Interfax reported.