WASHINGTON (AFP) - The US Senate confirmed former ExxonMobil chief Rex Tillerson as the next secretary of state Wednesday (Feb 1), handing a major boost to President Donald Trump as he builds his cabinet.

Tillerson was confirmed by a vote of 56 to 43, with four Democrats ultimately joining all 52 Republicans voting in favour. The vote was by far the closest in at least half a century.

Trump has repeatedly blasted Democrats for dragging out the confirmation process, and took to Twitter late Monday to accuse them of "delaying my cabinet picks for purely political reasons."

Tillerson, 64, had come in for severe criticism from Democrats who warned that his business approach and lack of government experience would hurt America's standing in the world.

But Republicans rallied around the nominee, after initial hesitation by Senators John McCain, Marco Rubio and Lindsey Graham about Tillerson's ties with Russia and his position on human rights.

"Mr Tillerson led a global enterprise with 75,000 employees, possesses deep relationships around the world, and understands the critical role of US leadership," Senate Foreign Relations Committee Chairman Bob Corker said in a statement.

"He has expressed a commitment to defend American values and to restore US credibility by strengthening old alliances and building new ones."

Democratic Senator Joe Manchin backed Tillerson, saying he will bring a "unique perspective to the State Department" and provide "wise counsel and objective advice to the president on our nation's foreign policy."

With Tillerson's confirmation and pending swearing-in, Trump will have several key members of his national security team in place, including Secretary of Defense James Mattis, Homeland Security Secretary John Kelly, CIA Director Mike Pompeo and US Ambassador to the United Nations Nikki Haley.