Mr Trump has repeatedly questioned the purpose of Nato, but, amid rising tensions with Russia, he called it a "bulwark of international peace and security" yesterday and hailed its role in the fight against terrorism.

He said "it would be a fantastic thing" if the US, Nato and Russia got along better but warned that "it may be just the opposite".

Mr Tillerson held a two-hour meeting with Mr Putin earlier yesterday in an attempt to to persuade the Russian president to abandon his unwavering support for Mr Assad following last week's chemical weapons attack.

However, on Wednesday night Russia vetoed a UN resolution condemning the sarin gas attack in Idlib province. Boris Johnson, the Foreign Secretary, said he was "dismayed" by the decision and that it put Russia "on the wrong side of the argument".