By Matt Frei
BBC News, Washington
The US government is reportedly seeking to tighten visa restrictions for British citizens of Pakistani origin.
The fertiliser bomb plot trial has brought the visa waiver into focus
Homeland Security Secretary Michael Chertoff had discussed options with London about revising the visa waiver programme, the New York Times said.
It follows the conviction of five men - mostly of Pakistani origin - for a UK bomb plot linked to al-Qaeda.
The UK Home Office said it would be unacceptable to "single out citizens of any particular background".
The fertiliser bomb plot convictions highlight a problem which has quietly dogged relations between the US and its closest ally ever since 9/11.
The following question is keeping US immigration officials awake at night:
If a few British men of Pakistani origin are prepared to blow themselves up and commit mass murder in the UK, how many will try and enter the US on the visa waiver programme which grants them visa-free access to America?
Put another way, could America's closest friend also harbour its most dangerous enemy and what should be done about it?
According to the New York Times report, Mr Chertoff has been discussing various options with London, none of which are considered palatable.
One is a blanket ban on the UK visa waiver programme, requiring more than a million annual visitors from Britain to apply for a visa.
This is bound to affect the tide of tourism, swelling on a cheap dollar, and is an idea that is bitterly resisted by the UK business community.
Another option is to require only Britons of Pakistani origin to apply for a visa.
But this would be seen as racial profiling which is something that the US authorities have always publicly resisted at home.
It would also be certain to embarrass the government in London.
Homeland security officials deny that any special talks have been taking place or that racial profiling is on the cards.
But they also point out that they are talking to congress about ways to strengthen the visa waiver programme which is authorised by law.