Asked about Trump's "Mission Accomplished" assertion, White said it pointed to the successful targeting of the three Syrian chemical weapons sites. European Union foreign ministers united to say they understood the need for the airstrikes and called for a new push for a political solution to the war in Syria.
Although officials said the singular target was Assad's chemical weapons capability, his air force, including helicopters he allegedly has used to drop chemical weapons on civilians, were spared.
That did not mean military strikes would continue.
May told legislators in the House of Commons that seeking their approval would have been impractical, both because Parliament was on a spring break until Monday and because some of the intelligence behind the decision was classified.
"The worldwide community is telling Russian Federation that either you make a decision on how you act and when you act, or the rest of us will make a decision in isolating you".
Although Israel has at times urged stronger USA involvement against Assad and his Iranian and Lebanese Hezbollah reinforcements in Syria, it voiced backing for Saturday's air strikes by Western powers.
President Donald Trump immediately said that Syrian President Bashar al-Assad would pay a "big price" and blamed both Russian Federation and Iran for supporting the Assad regime.
In Damascus, Syria's Deputy Foreign Minister Faisal Mekdad met inspectors from the global chemical weapons watchdog OPCW for about three hours in the presence of Russian officers and a senior Syrian security official.
Syrian forces recaptured the area from rebels over the weekend.
"We all know our work in Syria is not done", she said.More news: Winnipeg Jets prepare for first away game of series against Minnesota Wild
Instead, Syrian authorities offered them 22 people to interview as witnesses, he said, adding that he hoped "all necessary arrangements will be made ... to allow the team to deploy to Douma as soon as possible".
Monday's debate ended with a vote, forced by the SNP, on whether the House had sufficiently debated the matter of Syria.
Some of Trump's fellow Republicans also expressed unease over the potential for USA escalation in Syria without legislative input. Sen.
France and the US say the Geneva process is the only track to pursue a political resolution.
Her decision to authorise action without MPs' backing has been criticised by Labour leader Jeremy Corbyn, who said she could "easily" have recalled Parliament or delayed her decision until MPs returned to Westminster from the Easter recess. "We have done it because we believe it was the right thing to do - and we are not alone".
Mr Trump has also defended his use of the phrase "Mission Accomplished" to describe the US-led missile attack on Syria's chemical weapons program.
According to a statement, Putin and Iranian President Hassan Rouhani discussed the missile attack that targeted a science lab and two chemical weapons depots and agreed "that this illegitimate action has seriously damaged the prospects for a political settlement in Syria", the statement from the Kremlin said.
The trio of Western powers that carried out the strikes warned they would repeat the operation if Damascus used chemical weapons again, while Putin warned any fresh strikes would "provoke chaos".
Saturday's airstrikes have further aggravated relations between Britain and Russia, which were already at their lowest in decades following a nerve agent attack on a former Russian double agent and his daughter in England last month. Iran's Supreme Leader called the attack a crime and the country's Revolutionary Guard Corps said it gave "the resistance a more open hand", although it did not threaten to retaliate.
More than 70 delegations are expected at the April 24-25 donor conference for Syria in Brussels.