In a series of early morning tweets on Saturday, President Donald Trump accused his predecessor Barack Obama of wiretapping his New York office during the election campaign, but did not reveal the source of his information.

"Terrible! Just found out that Obama had my 'wires tapped' in Trump Tower just before the victory. Nothing found. This is McCarthyism!" he wrote at 6:35 am (1135 GMT).

Within minutes it was followed by three more Twitter posts in which Trump asserted without evidence that Obama had his phone calls intercepted and monitored.

"How low has President Obama gone to tapp [sic] my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick)guy!"

The tweets come as the new administration once again faces questions over the Trump campaign team's contacts with Russia prior to his inauguration.

Trump's first address to Congress this week was quickly overshadowed by the revelation that Attorney General Jeff Sessions - one of Trumptarget="_blank"'>