US citizens may require visas to enter the EU should the United States move ahead with plans to scrap visa-free travel for select EU nationals.

Twenty-eight member state ambassadors to the US made the threat on Monday (14 December) in an op-ed in The Hill after the US House of Representatives voted in support of the Visa Waiver Program Improvement Act of 2015.

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The US bill would ban certain EU nationals from entering the US without a visa if they had visited Iraq, Iran, Syria or Sudan after March 2011.

All four are seen as terrorist hotspots which attract "foreign fighters" - radicalised Muslims from Europe.

The US proposal follows the 13 November attacks in Paris by French and Belgian nationals. The terrorists, acting on behalf of Islamic State, killed 130 people and injured scores of others.

Fears are mounting in the US that foreign fighters may attempt to launch a similar attack on US soil.

A visa requires greater scrutiny, including face-to-face interviews at US consulates, and more paperwork.

“We want to make sure that terrorists don’t come to the United States," House majority leader Kevin McCarthy, a Republican from California, was quoated as saying in USA Today.

Under the bill, the US Department of Homeland Security can suspend countries from the visa free list if they are deemed a security risk.

Writing on behalf of the 28 ambassadors, the EU's top diplomat to the US, David O'Sullivan, said the legislation "could trigger legally-mandated reciprocal measures."

But O'Sullivan said such moves would most likely only affect legitimate travel by businesspeople, journalists, humanitarian or medical workers.

"Compulsory biometric checks at the port of origin would represent the de facto introduction of a visa regime in all but name; such indiscriminate action against the more than 13 million European citizens who travel to the US each year would be counterproductive, could trigger legally-mandated reciprocal measures, and would do nothing to increase security while instead hurting economies on both sides of the Atlantic," he wrote.

He noted the US visa waiver programme with EU member states already has built-in security features and that EU states want to improve information exchange and cooperation with the United States.

But O'Sullivan's pleas may not be enough to muster opposition to the new law.

The proposal still needs to pass the US Senate and to be signed into law by president Obama, but it has gained widespread support.

The US has a visa waiver programme with all EU member states except Poland, Romania, Bulgaria, Cyprus, and Croatia.