The United States currently has no plans to follow the UK in raising its terror threat level, the White House said.
The UK government had been in contact with their US counterparts over the decision, Press Secretary Josh Earnest said.
He said it was understood the threat level was raised in response to the danger posed by Islamic State fighters who have British passports.
The PM wants to confiscate passports. But in Cardiff they want to solve extremism at it's roots - they just can't get the help to do it.
David Cameron has unveiled a series of new measures to combat the threat of terrorism.
Rumours suggesting London's Tube network will be targeted in a terrorist attack on Monday are "completely untrue", police say.