The Syrian government and its ally Russia have blamed Israel for a deadly attack on a Syrian military airport.
Monday’s attack hit the Tiyas airbase, known as T4, near the city of Homs. Observers say 14 people were killed.
Israel, which has previously hit Syrian targets, has not commented. Syria initially blamed the US for the strike.
The incident comes amid international alarm over an alleged chemical attack on a Syrian rebel-held town. The US and France had threatened to respond.
US President Donald Trump said there would be a “big price to pay” for the alleged chemical attack in Douma, in the Eastern Ghouta region, near the capital Damascus. He branded Syria’s President Bashar al-Assad an “animal”.
But Russian Foreign Minister Sergei Lavrov said accusations that Mr Assad is behind the attack were a “provocation”.
Moscow favoured an “honest investigation” of such incidents but opposed apportioning blame without any proof, he added.
Meanwhile, Ahmet Uzumcu, head the Organisation for the Prohibition of Chemical Weapons, expressed “grave concern” about the alleged attack.
The OPCW is currently gathering information about the possible use of chemical weapons.
Could Israel be involved? Syrian state news agency Sana, quoting a military source, reported that air defences had repelled an Israeli missile attack on T4, saying the missiles were fired by Israeli F15 jets in Lebanese airspace.
Russia’s defence ministry said that, of eight missiles, five were shot down and three reached the western part of the aerodrome.
Israel rarely acknowledges carrying out strikes, but has admitted attacking targets in Syria dozens of times since 2012.
Its heaviest air strike on Syria, in February this year, included targeting the T4 air base.
That followed an incursion by an Iranian drone into Israel and the shooting down by Syrian air defences of an Israeli F16 fighter jet.
Israel has said it will not allow Iran, its arch-foe, to set up bases in Syria or operate from there, something Israel considers a major threat.
The Israeli military said Iran and its Revolutionary Guards had long been active in the T4 base, and were using it to transfer weapons, including to Lebanese Shia militant group Hezbollah, an enemy of Israel.
They also said the drone had been launched from the base.