Multiple explosions are being reported at Shayrat airbase, near Homs, in what some are calling an Israeli attack.
The base is one of the regime’s most significant installations in the center of the country.
Syria expert Charles Lister tweets that the base houses fighters from the Hezbollah terror group and the Iranian Quds Force.
In August, Syria said 31 regime and allied fighters were killed when a weapons delivery exploded.
In 2017, US airstrikes hit the base in response to a suspected sarin gas attack on the rebel-held town of Khan Sheikhun in northwest Syria that killed more than 80 people.
According to the Pentagon, US intelligence had established that the base was the launchpad for the alleged chemical attack.
Israel does not generally acknowledge individual sorties in Syria.