The US ambassador to the UN has said America is "prepared to do more" militarily in Syria but hopes it will not be necessary.
Speaking at an ill-tempered emergency UN Security Council meeting , Nikki Haley said Syrian President Bashar al Assad felt he could get away with using chemical weapons against his own people "because he knew Russia would have his back".
"That changed last night," she said, referring to US cruise missile strikes on a Syrian government airbase.
The strikes were in retaliation for a poison gas attack allegedly by Assad's regime which killed 80 people, including children.
US treasury secretary Steven Mnuchin said "additional sanctions" on Syria would be announced in the near future as part of the US' "ongoing effort to stop this type of activity and emphasise how significant we view this".
British ambassador Matthew Rycroft told the Security Council meeting that President Assad had shown the world he is "capable of redefining horror".
He called the US strike a "proportionate response to unspeakable acts".
In an unusually personal reply, the Russian representative accused Mr Rycroft of using "unprofessional" arguments and of lying.
:: Sam Kiley - Airstrikes branded 'game of American thrones'
He also requested a second chance to speak at the end of the meeting, asking Ms Haley to refrain from insulting his country.
The Russian representative, along with the Syrian and Libyan ambassadors, argued that America's unilateral military intervention defied the UN charter and violated international law.
The US, they said, had not acted in self-defence and had not sought the agreement of the Security Council, the UN body tasked with maintaining global peace and stability.
Russia said the White House had "completely ruined" the relationship between the two countries.
US secretary of state Rex Tillerson has described Russia's response to Friday's airstrikes as "disappointing but not surprising".
Fifty-nine Tomahawk missiles were fired from two warships - the USS Porter and USS Ross - in the Mediterranean Sea, targeting the government-controlled Shayrat airfield near the city of Homs.
The missiles struck targets including Syrian aircraft and fuel stations.
It was the first military intervention by the US against the Assad regime during the six-year civil war.
President Donald Trump said the strikes targeted the airbase from which the chemical attack on the rebel-held town of Khan Sheikhoun was launched on Tuesday.
Syria and Russia said several people were killed in the cruise missile strikes.
On Thursday, the Security Council abandoned negotiations on a resolution that condemned the use of chemical weapons and that demanded access to Syrian government flight logs and air bases from the day of the attack.
Moscow called the resolution "unacceptable".
Mr Trump had said during the presidential campaign that he would not be drawn into Syria's conflict. But the chemical attack changed his view on the situation, he said, as haunting images of harmed children shocked the world.
He called the attack "one of the truly egregious crimes" that "shouldn't have happened and it shouldn't be allowed to happen".
The Syrian government has denied responsibility and the Russian government warned against apportioning blame until an investigation had been carried out.
It comes as President Trump met China's President Xi Jinping for the first time, hosting the leader at Mar-a-Lago, his Florida home.