But Rex Tillerson stopped short of accusing the Russian government, saying he did not yet know if the attack was sanctioned by Moscow.
Following Britain's accusation that the attempted assassination of former spy Sergei Skripal and his daughter in the UK had originated from Russia, US Secretary of State Rex Tillerson followed suit and vowed that such action would "certainly trigger a response."
After discussing the incident with UK Foreign Affairs Secretary Boris Johnson on Monday, Tillerson released a statement saying he had "full confidence in the UK's investigation and its assessment that Russia was likely responsible."
"There is never a justification for this type of attack," Tillerson said in the statement. "And we are outraged that Russia appears to have again engaged in such behavior."
But Tillerson stopped short of formally accusing the Russian government, saying that he did not yet know if the attack was sanctioned by Moscow.
Tillerson's comments were firm compared to an earlier statement from White House press secretary Sarah Huckabee Sanders, who described the attack as "reckless, indiscriminate, and irresponsible."
After being pressed on whether Russia was responsible for the attack, Sanders said only that the US was "standing with our UK ally."
"I think they're still working through even some of the details of that, and we're going to continue to work with the UK," Sanders said.
Tillerson, who said the attacks "clearly came from Russia," offered some evidence to reporters on Monday, according to The Associated Press: "I cannot understand why anyone would take such an action. But this is a substance that is known to us and does not exist widely."
"It is only in the hands of a very, very limited number of parties," Tillerson continued.
Earlier on Monday, UK Prime Minister Theresa May confirmed that the deadly nerve agent was "Novichok," a chemical compound developed by Russia during the Cold War.
On March 4, Skripal and his daughter collapsed in a shopping centre in Salisbury, England and remain in critical condition.
Skripal, a double agent in the 1990s and early 2000s, passed Russian state secrets to British intelligence officials. He was pardoned after Russia agreed to trade four agents to the US and UK for 10 Russian agents in 2010.