The White House has blamed Russia for the poisoning of a former double agent and his daughter in the UK on March 4.
While Britain said Russia carried out the attack intentionally, or that the country had lost control of whoever had orchestrated the incident, the position of the US had been unclear.
US Secretary of State Rex Tillerson had pointed the finger at Russia but was fired the following day, and during a call with UK Prime Minister Theresa May on Tuesday US President Donald Trump only said that Russia must provide answers about the use of a chemical weapon in the UK.
And though White House Press Secretary Sarah Huckabee Sanders said Monday the attack was "reckless, indiscriminate, and irresponsible" she did not specifically blame Russia. But that position appeared to change on Wednesday.
"The United States shares the United Kingdom’s assessment that Russia is responsible for the reckless nerve agent attack on a British citizen and his daughter, and we support the United Kingdom’s decision to expel Russian diplomats as a just response," Sanders said.
UK Prime Minister Theresa May had given Russia a deadline of midnight Tuesday to explain how the chemical attack occurred. Having received no response from Russia, Britain retaliated by deciding to expel 23 Russian diplomats, freeze the accounts of Russians under suspicion in the UK, and cut high-level government contact between the two countries.
In turn, Russia immediately warned that its response will "not be long in coming."
But this is not the first time the Russian government has committed assassinations in the UK. Former Russian spy Alexander Litvinenko was poisoned in 2006 and a BuzzFeed News investigation found 14 deaths in the UK have been linked to Russia by US intelligence.
"This latest action by Russia fits into a pattern of behavior in which Russia disregards the international rules-based order, undermines the sovereignty and security of countries worldwide, and attempts to subvert and discredit Western democratic institutions and processes," Sanders said, adding that the US is working with allies to prevent "this kind of abhorrent attack" happening again.