WASHINGTON (AFP) - United States Vice-President Joe Biden, known as being prone to gaffes now and then, has compared some Republican lawmakers to Neanderthal cavemen.

Mr Biden was speaking on Thursday night at a reception marking the anniversary of a law designed to fight violence against women.

Mr Biden first drafted and defended the law 19 years ago as a US senator. It was renewed this year but only after a months-long fight in Congress, particularly in the House of Representatives, which is controlled by the Republicans.

Mr Biden said he was stunned that there had been debate on the law.

"I'm going to say something outrageous," Mr Biden said.

"The idea we still had to fight? We had to fight to reauthorise?" he mused.

Mr Biden blamed "this sort of Neanderthal crowd" in the House for stalling the legislation.

Mr Biden, 70, is known for oratory that sometimes gets him in trouble.

On March 23, 2010, when President Barack Obama was signing his landmark health-care reform into law, Mr Biden committed a classic open-mike blunder, whispering audibly into Mr Obama's ear "this is a big fucking deal".