Donald Trump accused his opponents of targeting him with "bull----" as he hit out at the Russia investigation at the biggest conservative conference of the year in Washington.

The US president slipped into attack mode after a damaging week of accusations by his former lawyer Michael Cohen and public humiliation of failed North Korea talks.

In his first public event since returning from Vietnam, he took aim at his critics, saying: "We're waiting for a report by people who weren't elected... And all of the sudden they try to take you out with bull----".

Referring to the special counsel leading the probe into potential collusion between the Trump campaign and Russia, he said: "Robert Mueller never received a vote and neither did the person who appointed him".

Mr Trump went on to hit out at Democrats, who now control the House of Representatives, saying: "They don't have anything on Russia so they now morph into 'let's inspect every deal he's ever done' .. they're sick."