US President Donald Trump is open to authorising additional strikes on Syria if the regime uses chemical weapons again or deploys barrel bombs in the country, the White House said on Monday.
"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," White House spokesman Sean Spicer told reporters.
Trump last week ordered missile strikes against an air field in Syria that US intelligence believes was used to carry out an attack with the chemical agent sarin.
The White House also doubled down on its rhetoric on the need for the Syrian regime leader to step down.
"You can't imagine a stable and peaceful Syria with Assad in charge," said Spicer.
TRT World's Tetiana Anderson reports.
Twenty percent of regime jets destroyed
US Defence Secretary James Mattis said on Monday that last week's US strike on a Syrian air base destroyed a fifth of the regime's working warplanes.
"The assessment of the Department of Defense is that the strike resulted in the damage or destruction of fuel and ammunition sites, air defence capabilities, and 20 percent of Syria's operational aircraft," Mattis said in a statement.
"The Syrian government has lost the ability to refuel or re-arm aircraft at Shayrat airfield, and at this point, use of the runway is of idle military interest," he added.
Earlier, the US military's Central Command spokesman Colonel John Thomas said the US strike at Shayrat airfield near Homs in central Syria had destroyed more than 20 Syrian jets.
Mattis called Friday's strike a "measured response" to the regime's "use of chemical weapons."
"The Syrian government would be ill-advised ever again to use chemical weapons," Mattis said.
Friday's strike saw two US destroyers unleash a volley of 59 tomahawk missiles at the air base.
Mattis said the runways were deliberately avoided because the United States was trying to draw a clear line that its military action was in response to the suspected chemical attack, and not a signal of willingness to get more involved in Syria's brutal civil war.