Mr Tillerson’s comments amount to the strongest US response yet to Theresa May’s declaration that it was ‘highly likely’ Russia was behind the poisoning of Sergei Skripal and his daughter Yulia in Salisbury on March 4.
The Prime Minister told MPs that the highly dangerous substance used in the attack was a military-grade Novichok nerve agent produced by Russia.
She set a deadline of midnight on Tuesday for Moscow to explain whether it was behind the attack or had lost control of its stockpile of the poison.
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.
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‘Those responsible – both those who committed the crime and those who ordered it – must face appropriately serious consequences.’