Members of Congress said Mr Trump's accusations require investigation or explanation.

Senator Ben Sasse, a Republican, described the allegations as serious and said the public deserved more information. He said in a statement it was possible that Mr Trump had been illegally tapped, but, if so, the president should explain what sort of tap it was and how he knew about it.

Representative Adam Schiff, the top Democrat on the House intelligence committee, called Mr Trump's assertion a "spectacularly reckless allegation".

"If there is something bad or sick going on, it is the willingness of the nation's chief executive to make the most outlandish and destructive claims without providing a scintilla of evidence to support them," Mr Schiff said in a statement.

As the furor unfolded a spokeswoman for Mr Trump said he was busy "having meetings, making phone calls and hitting balls" at his golf course in Florida.

Mr Trump's all-out attack on Mr Obama came five days after he accused his predecessor of being personally responsible for leaks suggesting links between Trump officials and Russia, and internal conflict in the new administration.

It marked a breach with previous assessments Mr trump had made of his relationship with Mr Obama.

Last month Mr Trump said: "We had a rough campaign, he was vicious during the campaign toward me and I was vicious to him. We said horrible things about each other. But it's a very strange phenomenon, we get along, I don’t know if he’ll admit this but he likes me."