Russia and the Syrian military blamed Israel for a strike early Monday on a major air base in central Syria, saying Israeli fighter jets launched the missiles from Lebanese airspace.
A war-monitoring group said the airstrikes had killed 14 people, including a number of Iranians active in Syria.
Russia's Defense Ministry said two Israeli aircraft targeted the T4 air base in Homs province, firing eight missiles. It said Syria shot down five of them while the other three landed in the western part of the base.
Syrian state TV quoted an unnamed military official as saying that Israeli F-15 warplanes fired several missiles at T4. It gave no further details.
Israel's Foreign Ministry had no comment when asked about the accusations.
Since 2012, Israel has struck inside Syria more than 100 times, mostly targeting suspected weapons' convoys destined for the Lebanese militant group Hezbollah, which has been fighting alongside Syrian government forces.
Most recently, Israel hit the same T4 base in February, after it said an Iranian drone that had violated Israeli airspace had been launched from the base.
The T4 base, which was used as a launch pad for attacks against Islamic State militants who were at one point stationed close by, is near the Shayrat air base, which was targeted by U.S. missiles last year in response to a chemical weapons attack.
Monday's missile attack came hours after U.S. President Donald Trump warned there would be a "big price to pay" for a suspected poison gas attack in an eastern suburb of Damascus.
Over the weekend, suspected chemical attacks killed at least 60 people and wounded more than 1,000 in Syria's rebel-held eastern Ghouta, a Syrian medical relief group said Monday.
The death toll is likely to rise, according to the Union of Medical Care Organizations, a coalition of international aid agencies that funds hospitals in Syria and which is partly based in Paris.
"The numbers keep rising as relief workers struggle to gain access to the subterranean areas where gas has entered and hundreds of families had sought refuge," the group said in a statement.
Initially, Syria's state news agency SANA said the attack on the T4 air base was likely "an American aggression," but Pentagon spokesman Christopher Sherwood quickly dismissed any U.S. involvement. The agency then shifted the blame to Israel instead.
SANA said the missile attack resulted in a number of casualties but provided no specific figures.
The Britain-based Syrian Observatory for Human Rights, which monitors the war through a network of activists on the ground, said 14 people were killed, including a number of Iranians and three Syrian officers.
Rami Abdurrahman, the Observatory's chief, said the assault targeted a mobile air defense unit and some buildings inside the air base. He added that it also hit posts outside the base used by the Iranians and Iran-backed fighters.
Israel fears Iran could use Syrian territory to launch attacks against it, after having repeatedly called for Israel's annihilation.
The U.S. launched several dozen Tomahawk cruise missiles at a Syrian air base last year, after a chemical attack in the northern Syrian town of Khan Sheikhoun killed dozens of people.
Saturday's suspected poison gas attack on the besieged town of Douma came almost exactly a year after the U.S. missile attack prompted by the Khan Sheikhoun deaths.
In recent weeks, government forces have recaptured villages and towns in the eastern Ghouta suburbs of the capital. Douma was the only town left holding out.
A 2013 chemical attack in eastern Ghouta that killed hundreds of people was widely blamed on government forces. The U.S. threatened military action but later backed down.
Syria denies ever using chemical weapons during the war and says it eliminated its chemical arsenal under a 2013 agreement brokered by the U.S. and Russia.
