The British Home Office says London remains on heightened terrorism alert, but there is no new information of specific targets, like the warnings issued this week in the United States.

Nonetheless, British police have advised security experts at some leading American financial companies, such as Citigroup, the Bank of America and Merrill Lynch, to be on guard for a possible terrorist attack on U.S. interests in London.

The warnings come after authorities in Pakistan found terrorist attack plans against the United States and Britain on the computer of a senior al-Qaida suspect arrested last month.

The information prompted the United States to increase security at several financial institutions, including the New York Stock Exchange and the World Bank and International Monetary Fund in Washington.

Leaders of Britain's opposition Conservative Party complain that while the United States is taking action, the British government is vague about the terrorist threat.

"We have a serious piece of information coming out from the United States relating to the specific targeting of buildings in New York," says Dominic Grieve, a Conservative Party spokesman on home affairs. "It is suggested that the information and intelligence they have received also refers to similar sites in London, and there is no government minister able to come forward either to provide the sort of information that been given in the United States, or indeed reassurance that that information isn't part of the intelligence and people should simply continue as before."

The Conservatives have been pressing Prime Minister Tony Blair to appoint a secretary for homeland security, as the United States did after the 2001 terrorist attacks.