The FBI has no specific information the men are plotting a terrorist attack, but they want to question them about possible connections to individuals who are involved in terrorism, the officials said, speaking only on condition of anonymity.
In Seattle, Dan Harrington told the FBI he rode a Greyhound bus across the border with one of the men whom agents want to question, reports Rick Price of CBS News affiliate KIRO.
"Now he was definitely on the same bus as me down from Canada," Harrington said, pointing to a photograph of Mustafa Khan Owasi. "And it was definitely Christmas Eve."
Harrington said federal agents detained Owasi during an unusually long delay at the border:
"I could hear the INS guy saying, 'Well basically that's not what you told me, your story keeps changing.' And they ended up leading him away," Harrington said.
Though he says Owasi never got back on that bus, which then continued to Seattle, Harrington finds it all disturbing. It's unclear what happened to Owasi after Harrington claims he last saw him.
Among the locations authorities were focusing their search on is New York, based on information received from at least one intelligence source, the officials said.
Because of the large gathering of Americans in New York City on New Year's Eve, authorities were taking the information seriously and pursuing the men even though there is no specific information that they are planning any activities, the officials said.
"We want to know why they are here. We want to question them ... and find out more," White House spokesman Scott McClellan told reporters in Crawford, Texas, where President Bush was vacationing.
McClellan said the information was developed in the ongoing investigation of terrorism, but he did not call the men suspects or terrorists. He said he would not comment on sources or methods of intelligence that tipped off authorities.
On Sunday, the FBI enlisted the public's help by putting out photos and names of five of the men they are seeking: Abid Noraiz Ali, Iftikhar Khozmai Ali, Owasi, Adil Pervez and Akbar Jamal, all born between 1969 and 1983.
The FBI warned that the names and birth dates may be false, reports CBS News Correspondent Jim Stewart.
"We have found that under the names that the FBI had provided to us there's no record of any of the five individuals as having ever applied for a U.S. visa," said State Department spokesman Philip Reeker.
The FBI said it had "no specific information that these individuals are connected to any potential terrorist activities, but based upon information developed in the course of on-going investigations, the FBI would like to locate and question these persons." It also said the men are believed to have entered the United States illegally on or around Christmas Eve.
Officials said the intelligence indicated the men crossed from Canada but that there was no specific information on what port of entry.
In New York City, 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.
One official said U.S. authorities' interest in them was heightened when an intelligence source provided information that some of the men being sought were connected to others who are the subjects of terrorism investigations.
The FBI said it was working with the Customs Service, the Immigration and Naturalization Service and the Transportation Security Administration to find the men.
INS spokesman Dan Kane said his agency has "implemented additional measures to look for these individuals."
The FBI is mindful that Al Qaeda used Canada as a gateway before during the Millennium plot to bomb Los Angeles International Airport. They're also aware that despite a forest of motion sensors and infa-red cameras, the 4,000-mile U.S-Canadian border is easily subverted.
Plus, the U.S. has long had its eye on a portion of the Middle Eastern population in Canada, which has a very lenient visa policy. According to one Canadian estimate, up to 50 suspected terrorist organizations had set up shop in Montreal alone.