Reports say several people have died or were injured after a military airport in Syria came under missile attack.
Several missiles struck the Tiyas airbase, also known as T4, near the city of Homs in the early hours of Monday, state news agency Sana said.
Details are still emerging and it is not clear who is responsible.
It follows international alarm over a suspected chemical attack on the rebel-held town of Douma.
US President Donald Trump branded Syria’s President Bashar al-Assad an “animal” on Sunday, warning that he, along with allies Iran and Russia, had a “big price to pay”.
Mr Trump and France’s President Emmanuel Macron issued a joint statement the same day vowing to “coordinate a strong, joint response” to the alleged attack.
But US officials have denied launching a missile attack.
“At this time, the Department of Defence is not conducting air strikes in Syria,” the Pentagon said in a statement.
“However, 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.”
Syria’s state news agency initially called the reported missile strike on the Tiyas airfield a “suspected US attack,” but later dropped the reference to the US.
In April 2017, the US fired 59 Tomahawk cruise missiles at Syria’s Shayrat military airfield in response to a chemical weapons attack on a different rebel-held town, Khan Sheikhoun.
Israel also carried out major strikes on Syrian targets earlier this year. The Israeli military has not yet commented on the Tayfur attack.