The White House on Monday condemned the poisoning of an ex-Russian spy in the U.K. earlier this month but declined to say whether Moscow was responsible.

“The use of a highly lethal nerve agent on U.K. soil is an outrage. The attack was reckless, indiscriminate and irresponsible,” White House press secretary Sarah Huckabee Sanders said.

Hours earlier, British Prime Minster Theresa May said it’s “highly likely” Russia was responsible for the poisoning of ex-Russian spy Sergei Skripal and his daughter.

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The White House did not go that far on Monday. Instead, Sanders said the administration is condemning the attack and “standing with our ally.”

“Right now we are standing with our U.K. ally. I think they’re still working through even some of the details of that,” Sanders said. “And we’re going to continue to work with the U.K., and we certainly stand with them throughout this process.”

May gave Russia until the end of Tuesday to respond to her allegations. If they do not respond, she said, the U.K. “will conclude that this action amounts to an unlawful use of force by the Russian state against the United Kingdom.”

May said she came to the conclusion based on an investigation of the chemical agent used in the attack in Salisbury and the knowledge that Russia has produced this agent before.

Russia reportedly dismissed the British claims a “circus show," a “provocation” and “nonsense,” even suggesting the attack on the Skripals may have been a false flag.

The Trump administration has faced criticism for its muted criticisms of Russia and Russian President Vladimir Putin after the U.S. intelligence community determined Russia sought to interfere in the 2016 presidential election.

The administration has not implemented sanctions against Russia that overwhelmingly passed both chambers of Congress last year.