Plans by Republicans in the US to 'repeal and replace' the so-called Obamacare healthcare system have collapsed.

Republican Senate leaders had been working to devise a replacement bill for several months.

However, with Democrats and independents universally opposing the proposals, they could afford to lose no more than two Republican votes in their efforts to pass the bill.

While some hard-line Republicans argued the bill did not go far enough, more centrist party members raised serious concerns over cuts to social healthcare programmes.

After two more Republicans announced their intention to oppose the bill in its current form - bringing the total to four - Senate Majority Leader Mitch McConnell said efforts to 'repeal and immediately replace' Obamacare had failed.

The bill will now not even go to a vote or be debated in the upper house.

McConnell said there would instead be a vote to repeal Obamacare without replacing - but US media reports that is very unlikely to succeed.

Despite the setbacks, Donald Trump - who has made healthcare one of his signature pledges - remained defiant, while blaming "all of the Democrats and a few Republicans" for the bill's failure.

He insisted, however, that the Republicans 'will return' for another effort.

Republicans should just REPEAL failing ObamaCare now & work on a new Healthcare Plan that will start from a clean slate. Dems will join in!

— Donald J. Trump (@realDonaldTrump) July 18, 2017