Michael Flynn, Donald Trump’s national security adviser, is facing mounting pressure over claims he may have broken the law by discussing US sanctions against Russia with a Moscow official before the US president’s inauguration.

The White House has been forced on to the back foot after the former general went from denying discussing sanctions with the Russian ambassador to Washington to saying he could not recall if the issue was addressed in conversations.

The Washington Post reported last week that US officials were concerned that Mr Flynn might have been signalling to the Kremlin that the Trump administration would adopt a softer stance on Russia than the Obama administration. The Federal Bureau of Investigation is probing the issue to determine what the two men discussed.