Downing Street insists the prime minister has been kept fully up to date on the crisis but opponents claim he is being 'blasé'.
Shadow foreign secretary Emily Thornberry, who is running to lead Labour, asked"is he afraid of angering Trump?" in an article in The Observer.
Mr Raab is expected to meet his French and German counterparts during the week before speaking to US Secretary of State Mike Pompeo in Washington on Thursday.
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