Syrian warplanes have reportedly taken off from the air base targeted by US air strikes, less than 24 hours after it was pounded by dozens of US cruise missiles.
Donald Trump ordered the strikes on the Shayrat base, near the city of Homs, in response to a chemical attack on the rebel-held town of Khan Sheikhoun earlier this week.
The Syrian government has been widely blamed for the attack, although it insists rebel groups were responsible.
The US Navy fired 59 cruise missiles at the base, killing at least seven people and causing what was described as extensive damage.
But within hours it was back in use according to the Syrian Observatory for Human Rights.
The London based monitoring group which uses sources on the ground to keep track of events in the country, said that Syrian army jets had taken off from the base to carry out strikes on rebel-held areas near Homs, .
They had "done the impossible" in order to continue using the base for sorties, the Observatory said.
The US air strikes triggered a major international row after they were angrily condemned by Russia.
Vladimir Putin’s government, which has consistently supported Syrian President Bashar al-Assad, said the strikes were a contravention of international law.
The US had carried out “an act of aggression against a sovereign state delivered in violation of international law under a far-fetched pretext", the Kremlin said.
Russian Prime Minister Dmitry Medvedev said the US had come “within an inch” of clashing with Russian forces.
Satellite imagery suggests the Shayrat base is home to Russian special forces and military helicopters.
The US said it gave Russia an hour’s warning before carrying out the strikes and deliberately avoided sections of the base where Russian soldiers and equipment are housed.