Citing a military source, the state-run Syrian Arab News Agency (SANA) said the attack had caused an unspecified number of deaths and injuries.
Syrian State TV said the T-4 airbase had been hit by "several missiles" in a "likely attack by the U.S.", early Monday morning local time.
Sen. John McCain, R-Ariz., on Sunday said President Trump's talk about pulling USA troops out of Syria "emboldened" Bashar Assad to launch a suspected chemical weapons attack.
The Syrian state denied government forces had launched any chemical attack. He tweeted on Sunday there would be a "big price to pay" and said Russian Federation, its president, Vladimir Putin, and Iran were responsible for enabling "Animal Assad".
In his tweets Sunday, Trump called Assad an "animal" and delivered a rare personal criticism of Russian President Vladimir Putin for supporting him.
"However, we continue to closely watch the situation and to hold those who use chemical weapons, in Syria and otherwise, accountable".
Facing military defeat, rebel groups in other parts of eastern Ghouta have taken safe passage to other opposition-held areas at the Turkish border.
McCain praised Trump for condemning the attack Sunday on Twitter, but said, "The question now is whether he will do anything about it".
"Yet again, there are reports of what appears to be a chemical weapons attack in Syria".
It follows global alarm over a suspected chemical attack on the rebel-held town of Douma.
Simply over a 12 months in the past, Trump ordered dozens of cruise missiles to be fired at a Syrian air base after declaring there was little doubt Assad had "choked out the lives of helpless" civilians in an assault that used banned gases.
"In Syria many forces, from various bodies and coalitions, are operating".
Basel Termanini, the USA -based vice president of SAMS, told Reuters another 35 people, majority women and children, had been killed at a nearby apartment building.
At least 40 people are reported to have died in the rebel-held town of Douma and if it is confirmed chemical weapons have been used by Bashar Assad's regime it could risk further escalating the crisis in the region.
This image, made from video released by the Syrian Civil Defense White Helmets, shows medical workers treating toddlers following the alleged poison gas attack in Douma.
The UK mission to the United Nations said on Sunday the Security Council was likely to meet on Monday afternoon over the attack, at the request of nine members: "UK, France, US, Poland, Netherlands, Sweden, Kuwait, Peru and Cote d'Ivoire have called an emergency meeting of #UNSC to discuss reports of chemical weapons attack in #Syria".
'Many dead, including women and children, in mindless CHEMICAL attack in Syria. The government has denied carrying out any such attack.
Analysts say this is President Assad's biggest military success since the fall of Aleppo in 2016.