Israeli forces bombed targets in and around Syria's T-4 airbase two months ago, after an Iranian drone controlled from the base entered Israeli airspace.
According to the Syrian news agency (SANA), the bombardment is targeted at the "T4" airbase in the Central Homs province exactly at 4 am local time (0100 GMT).
The slain militia were identified as Ammar Mousavi, Akbar Zavar Jannati and Mehdi Lotfi Naysar.
Russian Federation accused Israel of striking an air base in central Syria that killed 14, and two unnamed US officials reportedly confirmed that it was Israel that carried out the attack.
The Syrian government strongly denied it carried out a chemical weapons attack and the Organization for the Prohibition of Chemical Weapons said it has opened an investigation.
The Britain-based Syrian Observatory for Human Rights says that as of Monday night, troops have been on a 72-hour alert and are fortifying their positions.
On Monday, Iranian Foreign Ministry spokesperson Bahram Qassemi condemned the attack, which he called a "violation of Syria's sovereignty and territorial integrity" by Israel.More news: Despacito YouTube music video hacked plus other Vevo clips
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The evacuations follow a pattern of departures around the capital, Damascus, and other major Syrian cities as the government reasserts its control after seven years of war.
President Donald Trump called the airstrike "mindless" and blamed Russian President Vladimir Putin as "responsible" for supporting the attack.
According to some reports, "Hezbollah" has already reinforced its positions south of the Litani River, an area protected by the United Nations Interim Force in Lebanon (UNIFIL) under UN Security Council resolution 1701.
More than 500 people, mostly women and children, were brought to medical centres complaining of difficulties breathing, foaming at the mouth and burning sensations in the eyes. But it said the suffocations were the result of shelters collapsing on people inside them.
American officials denied any involvement in the air strikes, with a Pentagon spokesperson adding, "We continue to closely watch the situation and support the ongoing diplomatic efforts to hold those who use chemical weapons, in Syria and otherwise, accountable". Both Syria and Russian Federation have denied the Syrian government's involvement in that attack. Gen. Yuri Yevtushenko was quoted by Russian news agencies Sunday as saying Russia was prepared to send specialists to Douma to "confirm the fabricated nature" of the reports.
Meanwhile, the Syrian opposition blamed the Saturday's suspected chemical attack in the town of Douma on government forces.