The United States agreed with its ally Britain on Tuesday that Russia was probably behind an attempt to poison a former double agent, saying the perpetrators should face punishment.
"We have full confidence in the UK's investigation and its assessment that Russia was likely responsible for the nerve agent attack that took place in Salisbury last week," Secretary of State Rex Tillerson said.
"We agree that those responsible -- both those who committed the crime and those who ordered it -- must face appropriately serious consequences. We stand in solidarity with our allies in the United Kingdom and will continue to coordinate closely our responses."
Before issuing the statement, Tillerson called his British counterpart Foreign Secretary Boris Johnson to discuss the investigation into last week's attempt to kill former Russian spy Sergei Skripal and his daughter in the southwest of England.
Speaking during a flight back from Africa, Tillerson told reporters that British Prime Minister Theresa May's statement that the attackers had used a military-grade nerve agent developed by Russia appeared accurate.
"It appears that it clearly came from Russia. Whether it came from Russia with the Russian government's knowledge is not known to me at this point," he said.
"But you take a substance like was used, which is an extremely dangerous substance into another country, into a public place, where you know many others are going to be exposed is just -- it's almost beyond comprehension that a state, an organized state would do something like that.
"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. And I don't want to say anything further than that."
Asked whether the apparent attack on a NATO member would trigger an allied response, Tillerson said: "It certainly will trigger a response. I'll leave it that."