(CNN) US Ambassador to the United Nations Nikki Haley warned Friday that the United States "is prepared to do more" in response to Syria's use of chemical weapons and delivered a sharp rebuke to Russia for its support of the Syrian regime.

"The United States took a very measured step last night," Haley said. "We are prepared to do more. But we hope that will not be necessary. It is time for all civilized nations to stop the horrors that are taking place in Syria and demand a political solution."

Haley was speaking at a special UN session one day after the US military struck an airbase that served as home base for the Syrian planes that conducted the chemical attack that killed dozens of civilians, including children, earlier in the week.

Haley also slammed Russia, which has troops in Syria to support President Bashar al-Assad's regime. The council meeting took place as the United States and allies press for a resolution condemning the Assad regime for the bombing. Russia is likely to veto the resolution.

"Every time Assad has crossed the line of human decency, Russia has stood beside him," Haley told the council.

Russia "bears considerable responsibility" for Assad's use of chemical weapons, Haley said. "The joint investigative mechanism has found beyond any doubt that the Syrian regime has used chemical weapons against its own people multiple times," Haley said.

"Assad did this because he thought he could get away with it. He thought he could get away with it because he knew Russia had his back. That changed last night."

The US strike was the first direct military action taken by the US against the Assad regime in the country's six-year civil war . It represents a substantial escalation of the US military campaign in the region, and could be interpreted by the Syrian government as an act of war.

Russia's envoy to the United Nations slammed the US action, calling it "a flagrant violation of international law and an act of aggression" in remarks at a UN Security Council meeting on Friday.

Haley defended the strike Thursday, telling the Security Council that "there are times when states are compelled to take their own action." Preventing the spread and use of chemical weapons is in America's "our vital national security interest," she said.

Acting in her capacity as president of the UN Security Council, Haley then yielded the floor to Syria's Deputy UN Ambassador Mounzer Mounzer.

Mounzer maintained Syria "would never use such weapons in any of its operations against armed terrorist groups." The chemical attack killed more than 80 people, including 33 children, and injured more than 500, according to the Syrian Civil Defense group.

Responsibility, he hinted, lay with outside powers. "Let me stress that it is well known that those weapons have been used and stockpiled in many parts of Syria by terrorist armed organizations in cooperation or rather with a wink and a nudge by some ruling regimes in the region and outside, including Turkey, Saudi Arabia, Qatar and some European states," Mounzer said.

"They completely ignore all the facts and documented information on the use of chemical weapons by terrorists in many parts of the Syrian Arab Republic."

Russia slams US for strike

Russian Deputy Ambassador Safronkov warned that "the consequences of this for regional and international stability could be extremely serious." He was joined in his criticism by Bolivia's ambassador to the UN, Sacha Sergio Llorenti Soliz, who criticized the US of acting as "prosecutor," "judge" and "jury" in Syria.

"The United States not only unilaterally attacked, but while we were discussing here and demanding the need for an independent investigation an impartial investigation, complete investigation into the attacks, the United States has become that investigator, has become the prosecutor, has become the judge, has become the jury," said Soliz.

At one point, he held up a picture of former Secretary of State Colin Powell, and referred to Powell's 2003 presentation to the UN in which he pushed the Bush administration's case that Iraq had weapons of mass destruction, a claim that was never substantiated.

'Russia sits here today humiliated'

The United Kingdom, however, came out strongly in support of the US action.

The UK supports the US airstrikes "because war crimes have consequences and the greatest war criminal of all, Bashar al-Assad, has now been put on notice," United Kingdom Ambassador to United Nations Matthew Rycroft said.

"The US strike was a proportionate response to unspeakable acts that gave rise to overwhelming humanitarian distress, Rycroft said. "It was also a strong effort to save lives, by ensuring such acts never happen again."

Rycroft blasted Russia for its support of Assad.

"Russia has given Assad everything he could dream of," Rycroft said. "Without Russia's seven vetoes in the Security Council, defying the views of other members of this council, Assad would now have faced sanctions and justice."

He added, "Russia sits here today humiliated by its failure to bring to heel a puppet dictator, entirely propped up by Russia itself and Hezbollah and Iran."

UN Secretary General Antonio Guterres said all parties must remember their "shared duty to uphold international standards of humanity."

"Mindful of the risk of escalation, I appeal for restraint to avoid any acts that could deepen the suffering of the Syrian people," he said in a statement. "These events underscore my belief that there is no other way to solve the conflict than through a political solution."