Washington: US House Republicans passed legislation Wednesday that would ban abortions after the 20th week of pregnancy, a vote criticized by women's rights advocates but emblematic of conservatives' staunch pro-life position.

The House voted 242 to 184 in favour of the Pain-Capable Unborn Child Protection Act, with all but four Democrats opposed and all but four Republicans in favour.

The measure has little chance of becoming law. It faces a vote in the Senate, where Democrats can obstruct the bill, and should it reach President Barack Obama's desk it faces a possible veto.

Abortion remains a divisive issue in the United States and in Congress, where conservatives routinely introduce legislation, sometimes symbolic, that tightens restrictions on abortion.

‘We have no higher obligation than to speak out for those who can't speak for themselves, to defend the defenceless,’ said House Speaker John Boehner.

‘Late term abortions are agonizingly painful and they are happening all too often in our nation,’ added Republican Virginia Foxx before the vote.

The Supreme Court, in a 1973 ruling, legalised abortion up to the point of fetal viability, generally interpreted by states as up to 24 weeks.

Some states however have adopted laws setting the limit at 20 weeks after conception.

An earlier version of the bill failed in January when Republican women pulled their support over a requirement that women who had been raped report the incident to law enforcement before gaining access to care.

The revamped version removed that clause for adults, and would allow abortions in the case of rape or where the mother's life was in danger.

But House Democrat Jackie Speier said lawmakers should ‘stop playing doctor’ and leave medical decisions to a woman and her caregiver.

‘Women who go through these experiences go through them with so much pain and anguish, and here we are as members of this body trying to don another white coat,’ she warned.

The vote was held symbolically on the second anniversary of the conviction of US doctor Kermit Gosnell for killing three newborns, severing their spinal cords with scissors after failed attempts at late-term abortions, actions that horrified many Americans.

He is serving a life sentence in prison.

Republicans argue that the public is increasingly opposed to abortion.

But the proportion of Americans who want to ban abortion has held steady, from 22 per cent in 1975 to 21 per cent in 2014, according to Gallup.