Republicans muscled legislation through the US House tightening federal restrictions on abortions as thousands of pro-life activists marched outside.

The anti-abortion marchers converged on Washington in an annual protest against the 1973 US Supreme Court decision making abortions legal. The crowd of mainly young people marched to the steps of the Supreme Court which passed the Roe vs Wade decision.

The issue has long been one of the most bitter in America, pitting those who view abortion as the killing of a defenceless human being against those who argue women have the right to decide what happens to their bodies.

In the four decades since the Supreme Court ruling, the divide has not narrowed, with polls indicating Americans remain about evenly split over the issue.

The approved bill would permanently ban the use of federal money for nearly all abortions. It would also bar individuals and many employers from collecting tax credits for insurance plans covering abortion that they pay for privately and purchase through exchanges established under the Affordable Care Act.

The House had approved the same measure last year but it went nowhere in the Senate, then run by Democrats.

In a veto message, the White House said, "The administration strongly opposes legislation that unnecessarily restricts women's reproductive freedom and consumers' private insurance options."