Five foreign nationals who are being sought by the FBI for questioning, and who may have entered the United States illegally from Canada, are connected to a passport smuggling operation with possible ties to terrorists, U.S. and Canadian officials said yesterday.

The biggest concern among U.S. officials is the possibility that the men, who are believed to have lived in Pakistan, could be part of a larger group that is planning a terrorist attack on or around the New Year, officials said.

A notice issued Sunday by FBI Director Robert S. Mueller III asked law enforcement agencies and the public for help in seeking five foreign nationals identified as Abid Noraiz Ali, Iftikhar Khozmai Ali, Mustafa Khan Owasi, Adil Pervez and Akbar Jamal.

All are believed to have been born between 1969 and 1983, but the FBI warned that the names and birth dates may be false. It also said the men are believed to have entered the United States illegally on or around Christmas Eve.

The FBI notice said the government had "no specific information that these individuals are connected to any potential terrorist activities."

But the notice was labeled as part of the "War on Terrorism" on the FBI's Web site, and White House spokesman Scott McClellan said yesterday that the notice was "based on information developed in the course of ongoing investigations relating to the war on terrorism."

"Any time we have five individuals like this who enter the country illegally, we want to know why they are here, we want to question them," McClellan said. "And that's why the FBI has enlisted the help of the public."

One source familiar with the ongoing investigation said the five men were part of a group of 19 individuals who had sought fake documents in order to enter the United States. The Sept. 11, 2001, terror attacks were carried out by 19 hijackers who were members of Osama bin Laden's al Qaeda terror network.

But several other U.S. officials strongly disputed that account, saying the FBI had no firm grasp on the precise number of men who may be connected to the illicit smuggling ring and whether they were definitively linked to terrorism.

The original information about the five men, along with their pictures, came from Canadian authorities who sent the data to the FBI last week, U.S. officials said. Although the FBI immediately transmitted the information to the Immigration and Naturalization Service, the Customs Service and the Transportation Security Administration, the men were already believed to have entered the United States on or about Christmas Eve, officials said.

No direct links have been found between the five men and terrorist activities, officials said. But one U.S. official said the men had ties to others with suspected terrorist credentials, including those involved in the smuggling operation.

"If there is a plot, this is a way of letting them know that we are on to them and we are looking for them," one law enforcement official said. "We now have the whole country keeping an eye out for them."

In New York, police spokesman Michael O'Looney said the department has "increased its counterterrorism efforts" as a result of the FBI warning and shared the names and photographs of the five men with its various police commands.

Paul Marsh, a spokesman with the Royal Canadian Mounted Police, declined to comment in detail on the FBI alert. "We are aware of the interest expressed by U.S. law enforcement agencies in these individuals and we are helping in any way we can," Marsh said.

Michel Juneau-Katsuya, a retired senior counterterrorism official with the Canadian Security Intelligence Service (CSIS), said that if the five men are terrorists, they almost certainly have split up by now and are laying low through disguises or other means. They are also probably receiving help from other associates, he said.

"We could be in serious trouble if these are people with bad intentions," Juneau-Katsuya said. "This is the New Year, a time of big public gatherings and therefore a time offering possible mass casualties in any attack."