US Republican presidential nominee Donald Trump hit back at President Barack Obama on Tuesday evening after he was accused of being unfit to take office.

Obama criticised the billionaire candidate earlier in the day for criticising the Muslim family of a US Army captain who was killed while serving in Iraq.

The spat between Trump and the Khan family started last week when Khizr Khan, the father of the dead soldier, attacked the Republican nominee for calling for a ban on Muslims entering the US.

Trump responded to Khan by accusing him of silencing his wife Ghazala, who did not speak while standing beside her husband at the Democratic National Convention.

Ghazala Khan later denied Trump’s claim, saying that she chose not to speak because she was overcome by emotion when she saw her son’s picture.

Trump’s attitude towards the Gold Star family triggered a wave of criticism, even from those supporting his presidential campaign, including Speaker of the House of Representatives Paul Ryan, Senate Republican leader Mitch McConnell, Senator John McCain.