Britons travelling to Lucknow have been warned to take extra care and to consider postponing visits to holy sites in the city.
The Foreign Office advice on Monday came after a Shia cleric and his followers warned British, American and Israeli citizens to stay away. However, the statement did not identify the cleric or his organisation in Uttar Pradesh.
The Foreign Office said: "You should exercise caution in visiting such sites and may wish to consider postponing visits until the situation becomes clearer." The US has also issued a warning for its citizens to avoid these sites.
The unnamed cleric and his followers had issued statements over the war in Iraq and notices "banning" visitors from US, UK and Israel were posted at some sites. The signs said: "The entire Muslim community is aggrieved by damage done to the holy shrines of Hazrat Ali at Najaf and Imam-e-Husain, Karbala, in Iraq due to firing by the American and British coalition forces."
"These religious monuments at Lucknow are the only replicas of the original in Iraq. We cannot allow the original religious places to be damaged and replicas to be visited by tourists."
The general Foreign Office travel advice on India maintains that there is a continuing risk of terrorism in India but adds: "Over 400,000 British tourists visit India every year. The vast majority of these visits are trouble-free. However, we strongly recommend that you remain vigilant in all parts of India."
It strongly advises against travel to Jammu and Kashmir, with the exception of Ladakh via Manali or by air to Leh.