NEW YORK, May 22: The US authorities and New York Police put the city on a high alert on Tuesday following unverified reports of threats against two of city’s landmarks - the Brooklyn bridge and the Statue of Liberty.

The threats followed statements by US Vice President Dick Cheney on Sunday that attack against US targets by terrorists was a real possibility and on Tuesday Defence Secretary Donald Rumsfeld told the US Senate that terrorist groups could obtain weapons of mass destruction from countries like Libya, Iran, Iraq or North Korea.

The FBI Director, Robert Mueller, also said on Tuesday that it was inevitable that suicide bombers would strike in America.

The New York police began operating checkpoints at many of the city’s major bridges and tunnels on Monday night, causing traffic jams and resurrecting memories of a city under siege after the collapse of the World Trade Center.

Well into last night, officers were stopping any car or truck that they deemed suspicious, while police boats patrolled the waters under the Brooklyn and Manhattan Bridges and around Liberty Island. Police officials said that these checkpoints and patrols would continue indefinitely.

Police Commissioner Raymond W. Kelly referred to the information as “general threats to New York City” and said the police “are taking all necessary precautions and are communicating with the appropriate law-enforcement agencies on both the state and federal levels.

“When asked how people should respond to these warnings, Mr Kelly said, “People should take this in the sense that government is reacting to information, doing what it thinks is prudent, and they should continue to go forward with their lives.”

On Wednesday the police shut down the Brooklyn bridge for an hour when someone spotted a suspicious package lying on the bridge.

The bridge, which links Manhattan Island to the borough of Brooklyn over the East River and is a major New York City landmark, was closed at about 5am (0900 GMT) but reopened at around 6:05am (1005 GMT).

“There was no major problem (with the package), no bomb or anything,” a spokeswoman for the department said.

New York was already on heightened alert as it prepared to kick off on Wednesday the annual “Fleet Week” ahead of the Memorial Day holiday weekend.

More than 6,000 sailors, Marines and Coast Guard personnel and about 22 ships, including six warships, were expected in the city.

The New York Governor, George Pataki, in a statement on Tuesday urged the people to go about their business.

“We’ve been in touch with federal officials through our Office of Public Security and I want to strongly urge New Yorkers today, tomorrow, this weekend, next week and thereafter to go around and go about their ordinary lives,” Pataki said.

Senior Bush administration officials have stepped up their warnings that extremists could launch new attacks.