The prime minister revealed on Monday the nerve agent used on former KGB colonel Sergei Skripal and his daughter Yulia was likely to have been developed by the Soviet military during the 1970s and 1980s.
Mrs May said it was “highly likely” Moscow was to blame for the attack which left Mr Skripal and his daughter in hospital in a critical condition after they were found unconscious on a bench in Salisbury.
She has given Russian president Vladimir Putin until the end of Tuesday to explain what happened or face what what she said were “much more extensive” measure against the Russian economy.
Donald Trump has been a strong supporter of the Kremlin since he took office last year and has refused to speak out against Russia in the past, so what has the White House reaction been to the attack on UK soil?
Will Donald Trump stand by UK if war breaks out?
The White House has condemned the “reckless and indiscriminate” attack in Salisbury, however they have fallen short of outright blaming Russia for the attack.
In a briefing on Monday, White House press secretary Sarah Huckabee Sanders said: “We’ve been monitoring the incident closely, taking it very seriously. The use of a highly lethal nerve agent against UK citizens on UK soil is an outrage.
“The attack was reckless, indiscriminate and irresponsible. We offer the fullest condemnation and we extend out sympathy to the victims and their families and our support to the UK government.
“We stand by our closet ally and the special relationship that we have.”
Russian spy attack: Press secretary Sarah Huckabee Sanders avoided blaming Russia for the attack
However at the briefing she was pressed whether this meant Russia was responsible, she replied: “Right now, we are standing with our UK ally.
“I think they’re still working through some of the details of that, and we’re going to continue to work with the UK.”
When asked to be more specific, she said: “We stand with our ally and we certainly fully support them and are ready if we can be of any assistance to them.”
The president has avoided criticising Russia since taking office last year and has also refused to impose sanctions on Moscow.
Russian spy attack: Theresa May speaking at the House of Commons about the attack on Skripal
The Atlantic has reported the response by the US government to the attack has been meek and far from the outrage expected from previous governments.
The default reaction would be to offer technical assistance to the UK, such as forensic chemical analysis, a visible show of solidarity, and a carefully coordinated statement following Theresa May’s announcement it was “highly likely” Russia was the perpetrator.
This would be followed by a NATO statement and a cooperation by the US to impose the same sanctions as the UK, the Atlantic reports.
However none of these actions have occurred more than a week after the poisoning, although it was also reported it may be too early to say whether this means the Trump administration will do nothing.
Russian spy attack: Police in Salisbury tracing the trail of the nerve agent
In contrast, US Secretary Rex Tillerson said the nerve agent attack “clearly came from Russia” and will “certainly trigger a response.”
Mr Tillerson’s comments amount to the strongest US response after he told journalists travelling with him in Africa the Novichok agent was “only in the hands of a very, very limited number of parties.”
In a formal statement released after a phone call with Foreign Secretary Boris Johnson, the US Secretary of State said: “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.
“Those responsible – both those who committed the crime and those who ordered it – must face appropriately serious consequences.
Russian spy attack: Sergei Skripal and his daughter Yulia remain in hospital in a critical condition
“We stand in solidarity with our Allies in the United Kingdom and will continue to co-ordinate closely our responses.”
Recently the special relationship has become strained, most notably when Theresa May condemned Trump’s Islamophobic retweets of the far-right group British First.
A spokesman for Downing Street said at the time: “It is wrong for the President to have done this.”
The White House has stopped short of pointing the finger at Russia for the attack on Sergei Skripal and his daughter, whereas France, Germany and the US Secretary of State have all given their backing to the UK.
It remains to be seen whether the US will offer any support to the UK, but according to critics, Trump’s inaction to speak out against the Kremlin indicates where his stance and support is.