United States President Donald Trump has said he is prepared to accept the outcome of the country's midterm elections and work with Democrats following significant Republican losses that handed the opposition control of Congress.

Trump made the remarks during a telephone interview with The New York Times on Tuesday night, as he monitored election results at the White House.

Asked whether he would accept the results, the President said he was “absolutely willing” to do so, adding that his administration would look forward to working with Democrats.

“We’ll probably work something out,” he said.

Trump attributed the Republican Party's poor performance partly to his absence from the ballot, arguing that the outcome would have been different if he had contested the election.

He also defended his decision to launch military action against Iran, describing it as a “very wise decision”.

The President said he had no regrets about endorsing Republican candidates who lost their Senate races, including Darline Graham of South Carolina and Texas Attorney-General Ken Paxton.

Speaking shortly before 10:30 p.m., Trump said he was following the results as the interview progressed.

“I’m just looking at these results as I’m talking,” he said, reacting to Graham's defeat. He also questioned how her brother, the late Senator Lindsey Graham, would have performed had he contested the election.

Democrats secured control of the Senate and were projected to take the House of Representatives, reversing Republican dominance of both chambers and creating a new political balance in Washington.

The outcome is expected to affect the President's legislative agenda during the remaining years of his second term, as Democrats prepare to assume control of congressional proceedings and oversight.

The US midterm elections are held halfway through a president's four-year term, with voters choosing members of Congress, state officials and local representatives.