According to UPI, Syria "vowed to retaliate after an apparent Israeli airstrike on the capital Damascus early Sunday. A government official said on CNN the attack on a military research facility was "an act of war" that the government would not take lightly. "Syria is a country that does not accept insults and it doesn't accept humiliation," said Omran Zoabi, Syria's information minister. Zoabi added the attack had opened "a wide door for all possible options." It remains to be seen what, if any, option Syria will take or if it will merely jawbone toothlessly, inviting further unrequited air-based incursions into its territory. Most likely any response will need the preapproval, and the assistance, of Putin.

Incidentally, the only response so far has come from Israel. As Stratfor reports, citing Israel News, the airspace in northern Israel has been closed until May 9 due to an Israel Defense Forces directive issued May 5. Which means the only planes flying in north Israel, which borders Syria through the Golan Heights, would be military.