Officers along the U.S.-Canadian border and on New York City's streets are being extra vigilant for five men of Middle Eastern origin who may have crossed the border into the United States on Christmas Eve.

Officials have not ruled out a connection to a terrorist plot or cell, but they could not confirm a link, either. White House spokesman Scott McClellan said Monday the intelligence that triggered the search came from an anti-terrorism investigation.

FBI spokesman Ed Cogswell said the information came from an investigation into a worldwide passport smuggling ring. He said the subjects of the manhunt are not those who ran the operation but probably are people who may have been smuggled across the border, Cogswell said.

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 and living in the Toronto area for several days before being smuggled into the United States by car.

The National Post in Canada reported that a British Columbia woman said she told the FBI on Monday that she saw two of the wanted men on a Vancouver Island ferry on Dec. 10.

The FBI released photographs of five men Sunday in hopes they would be recognized. Cogswell acknowledged the FBI is uncertain about the names and birth dates released with the photos, or even that the men entered the country.

Nonetheless, federal and local officials are taking no chances.

Customs Service spokesman Dean Boyd said inspectors along the U.S.-Canada border are asking travelers more questions and increasing the number of vehicle and cargo inspections.

New York City police spokesman Michael O'Looney said his department has increased its counterterror efforts as a result of the FBI warning and distributed names and photographs of the five men to its various police commands.

The search comes just before large crowds gather for New Year's Eve celebrations, especially in New York's Times Square. The nation's color-coded terrorism alert system remained at yellow, the middle of five levels.

In Crawford, Texas, where President Bush is spending time at his ranch, McClellan told reporters the information on the five men was developed "in the course of ongoing investigations relating to the war on terrorism."

"We don't have any specific information that ties them to terrorist activity, but we do believe they have entered this country illegally," he said. "And any time anybody enters the country illegally, we want to know why they're here, and we want to question them."

McClellan said he would not comment on sources or methods of intelligence that tipped off authorities. The Toronto Star said the FBI was alerted by Canadian authorities.

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.

The FBI said it was working with the Customs Service, the Immigration and Naturalization Service and the Transportation Security Administration to find the men.

Cogswell said the FBI does not know where the five are from, but they are believed to be of Middle Eastern origin. He said border agencies had not had information that the men might try to enter the country.

Anyone with information was asked to contact the nearest FBI office.