Donald Trump's former campaign chairman has met Senate investigators, giving his recollection of a Trump Tower meeting with a Russian lawyer and agreeing to turn over contemporaneous notes of the gathering last year, sources said.

Microsoft is investing heavily in research and development as it prepares for a software revolution, Bill Gates told the North's Economy Minister Nigel Dodds at a meeting in the US today.

A United States Senate panel, following the House of Representatives' lead, has authorised subpoenas for White House political adviser Karl Rove and other top aides involved in the sacking of federal prosecutors.