The Foreign Office has warned Britons in the United States to remain vigilant amid fears that terrorists are plotting an attack on the 10th anniversary of the 9/11 atrocities.
American counter-terrorism officials are investigating a "credible but unconfirmed" report that al Qaida is planning a car bomb strike on bridges or tunnels in New York or Washington.
The US has been put on heightened security ahead of Sunday's landmark anniversary of the September 11, 2001 suicide attacks which killed 2,977 people, including 67 Britons.
The Foreign Office has updated its advice for British nationals living and travelling in America to take account of the latest terror threat intelligence, although it did not warn against visiting any parts of the country.
The advice says: "There is a general threat from terrorism in the United States. Attacks could be indiscriminate, including in places frequented by expatriates and foreign travellers.
"In light of the publicity surrounding the anniversary of the 9/11 attacks, we remind British nationals of the global threat of terrorism and need to remain vigilant."
British officials say there has been no change to the assessment of the threat level posed to the UK by international terrorism, which was reduced from "severe" to "substantial" in July, meaning an attack is considered a "strong possibility".
