Donald Trump's senior adviser has suggested Barack Obama could have spied on the President using a microwave.

Kellyanne Conway says she has no evidence to support Mr Trump's claim that the former president "wiretapped" Trump Tower phone lines during the election.

She pointed to recent revelations about government surveillance to suggest it was possible Obama used a different technique.

Speaking to US newspaper The Record, she said: "What I can say is there are many ways to surveil each other now, unfortunately, including microwaves that turn into cameras, et cetera.

"So we know that that is just a fact of modern life."

But she told 'Good Morning America' that she "wasn't making a suggestion about Trump Tower".

She said she was answering a question about surveillance "generally", and without specific reference to the current spying claims.

The White House intelligence committee asked the administration to provide evidence of Mr Trump's allegation by Monday.

Ms Conway told ABC's 'Good Morning America': "The answer is I don't have any evidence and I'm very happy that the House intelligence committee (is) investigating."

She later tweeted that the administration is "pleased" with the ongoing congressional investigation and "will comment after."

Trump's critics have slammed the president for making the wiretapping claim on his Twitter account without evidence.

Wiretapping a US citizen would require special permission from a court, and Mr Trump, as president, would have the ability to declassify that information.

James Clapper, who was Obama's director of national intelligence, has said that nothing matching Mr Trump's claims had taken place.