The White House has refused to follow Theresa May’s lead in blaming Russia for the poisoning of a former spy and his daughter in Salisbury.
However, the US later acknowledged the attack ‘clearly came from Russia’ in comments made by Secretary of State Rex Tillerson.
He warned that the poisoning ‘will trigger a response’.
Earlier, the White House finally broke its silence over the attack, describing it as ‘reckless, indiscriminate and irresponsible’.
But Donald Trump’s spokeswoman Sarah Huckabee Sanders stopped short of saying that Russia was responsible for the incident that left Sergei and Yulia Skripal critically ill.
Her comments came hours after Theresa May said the nerve agent used in the poisoning was developed by Russia, and it is ‘highly likely’ that Russia is responsible.
Sanders described the incident as ‘an outrage’ and said Washington has been closely monitoring developments.
She said the US stands by its ally and is ready to offer assistance.
Sanders said: ‘The use of a highly lethal nerve agent against UK citizens on UK soil is an outrage.
‘The attack was reckless, indiscriminate and irresponsible.’
Donald Trump has not tweeted about the incident in the eight days since the Skripals were found slumped on a bench in Salisbury.
It has since emerged that they were exposed to a ‘military grade nerve agent’ developed by Russia, Mrs May told MPs in the House of Commons earlier.
She said: ‘This was not just a crime against the Skripals, it was an indiscriminate and reckless act against the United Kingdom, putting the lives of innocent civilians at risk.’
A Downing Street spokesman said the prime minister May has spoken with President Emmanuel Macron of France and both agreed that ‘French and British governments should coordinate closely as the investigation developed’.