A US air strike in response to a suspected chemical attack damaged or destroyed 20% of Syria’s operational aircraft, the US has said.
Defence Secretary James Mattis said Syria would be “ill-advised ever again to use chemical weapons”.
Syria has denied a chemical attack on the rebel-held town of Khan Sheikhoun last week that left 89 people dead.
G7 nations are meeting in Italy to discuss policy and how to persuade Russia to abandon its Syrian ally.
The US fired 59 cruise missiles at Syria’s Shayrat airbase last Thursday, following the suspected chemical attack a day before.
Mr Mattis said the “measured response” by the US had “resulted in the damage or destruction of fuel and ammunition sites, air defence capabilities and 20% of Syria’s operational aircraft”.
He added: “The Syrian government has lost the ability to refuel or rearm aircraft at Shayrat airfield and at this point, use of the runway is of idle military interest.”
The Syrian military admitted significant material damage but a Russian defence ministry spokesman said only six Syrian Air Force MiG-23s, plus a number of buildings, were destroyed and that only 23 of the missiles had reached Shayrat.
Mr Mattis said the strike had shown the US would “not passively stand by while [Syrian President Bashar al-Assad] murders innocent people with chemical weapons”.
White House spokesman Sean Spicer said further strikes were on the table.
“The sight of people being gassed and blown away by barrel bombs ensures that if we see this kind of action again, we hold open the possibility of future action,” he said.
Meanwhile, the Associated Press news agency quoted a senior US official as saying that the Russians knew of the chemical attack, because a drone had been flying over a hospital in Khan Sheikhoun as victims sought help. Hours later a jet bombed the hospital in what the US believed was an attempt to cover up the attack, the agency said.