Mr Trump was said to be "agitated" by the reluctance of conservative Republican congressmen to vote for the American Health Care Act because they do not believe it goes far enough in dismantling Obamacare.

Republicans have a majority in the House of Representatives but they can only afford to lose 21 votes from their own side. Democrats will all vote against the bill.

However, with only hours to go before an expected vote at least 35 Republicans still planned to vote against, despite last minute concessions from Mr Trump and his allies.

Defeat would be a huge setback to for the president who wrote the "Art of the Deal" and was elected in part on the promise of his negotiating skills.

Failure on this landmark proposal would install doubts about his ability to carry his own party on other major platforms of his campaign,like tax reform and infrastructure investment. Global financial markets were monitoring the vote closely.

The promise to repeal Obamacare was key to Republicans keeping control of Congress, and to winning the White House, in November's election.

The bill has been held up by members of the Freedom Caucus, a conservative group of Republican politicians. Congressman Mark Meadows, chairman of the Freedom Caucus, said there was "No deal" with the Republican leadership.

On Friday morning Mr Trump taunted the group for their opposition to the bill, accusing them of being insufficiently against abortion.

“The irony is that the Freedom Caucus, which is very pro-life and against Planned Parenthood, allows P.P. to continue if they stop this plan!” he tweeted, referring to the women's healthcare clinics that would have their funding cut under his healthcare proposal.