Federal authorities received unsubstantiated information that terrorists could launch a maritime attack on New York City, a threat taken seriously because of the large crowds that gather in Times Square on New Year's Eve, a Homeland Security Department official said Tuesday.

Gordon Johndroe, a spokesman for the new agency, said the government was reacting similarly to July 4, when security was increased mainly because of the crowds rather than information from specific threats.

Johndroe said the information on the new threat was "unsubstantiated, uncorroborated and of suspect credibility."

There are no plans to raise the nation's threat level above yellow, the middle of a five-tiered color-coded rating system, Johndroe said.

Meanwhile, President Bush said Tuesday he personally ordered the FBI to begin a nationwide hunt for five men believed to have entered the country from Canada on Christmas Eve.

Speaking in Crawford, Texas, where he's vacationing at his ranch, Bush said U.S. authorities need to know what the men are doing in the United States.

"We don't have any idea of what their intentions might be, but we are mindful that there are still some out there who would try to harm America and harm Americans and so therefore we take every threat seriously, every piece of evidence seriously," Bush said.

The FBI on Sunday released photos, names and birth dates of the five and sought the public's help tracking them down for questioning. However, bureau officials acknowledge they are not certain that the identities and ages are correct.

The five, described by the FBI as men of Middle Eastern origin, may have fake passports since the information that led to the FBI bulletin came from an investigation into an illegal passport scheme.

The names released by the FBI are: Abid Noraiz Ali, Iftikhar Khozmai Ali, Mustafa Khan Owasi, Adil Pervez and Akbar Jamal. Each has a purported birth date between 1969 and 1983.

All remained at large Tuesday.

Sen. Hillary Rodham Clinton, D-N.Y., told a news conference Tuesday it's believed the five crossed the border into New York state with false documents. She said the Department of Homeland Security needs to establish an office dedicated to improving security along the nation's northern border.

The Toronto Sun, quoting police sources in Canada, said the men arrived at Toronto's Pearson International Airport about two weeks ago, claiming refugee status. They stayed in the Toronto area for several days before being smuggled into the United States by car.