WASHINGTON -- President Clinton's national security adviser urged Americans to be "vigilant" against potential terrorist attacks at home and abroad over the holidays.
Sandy Berger, head of the National Security Council, said Sunday that authorities still were seeking to determine whether an Algerian arrested on charges of bringing a trunkful of bomb-making explosives into the country from Canada was part of a terrorist network.
"We're not aware of any other specific threat against particular targets in the United States," Berger said on CBS' "Face the Nation." "Obviously, if that changes, we'll alert the American people."
Nervous U.S. officials are attempting to determine whether there is any connection between Saudi Arabian militant Osama bin Laden and Ahmed Ressam, 32, who was caught trying to cross from Canada into Washington state Tuesday with 100 pounds of bomb-making supplies.
Even Ressam's arrest in PortAngeles, Wash., and recent crackdowns in Jordan and Pakistan against potential anti-U.S. terrorists "certainly don't eliminate the threat . . . and you don't know what else is being planned," another senior official said.
Pakistani authorities have arrested at least 200 people they fear may try to attack U.S. citizens in Pakistan, an intelligence official in Islamabad confirmed Sunday. Security at Pakistan's international airports has been tightened to try to track followers of bin Laden, who is based in Afghanistan, the official said.
The arrests were made during a series of overnight raids in northwestern Peshawar, which borders Afghanistan, and in the federal capital of Islamabad, they said. Most of those detained were Afghan nationals.
They have been held for interrogation following reports that bin Laden's supporters may attack American targets in Pakistan or use Pakistan as a transit route to other attack sites, said the official.
Similar arrests were made in Jordan in recent weeks.
"The detention of these people doesn't mean that they were about to launch a terrorist strike in Pakistan," said another intelligence official, who stressed that the arrests were "preventive in nature."
"With a sizable population of anti-U.S. religious elements in the country, we just can't take any chances," the official said.
In Montreal, authorities found an orange van registered to Benni Norris, the name on a passport Ressam was carrying when he was arrested Tuesday, and a bomb squad was called to investigate the 1989 GMC cargo van.
On Saturday, the U.S. Customs Service placed all 301 ports of entry into the United States on high alert in response to Ressam's arrest.
A supervisor at the Peace Bridge said Sunday that drivers crossing the local international bridges shouldn't notice any difference in the way they're questioned when entering the United States.
"The questions are pretty much all the same. We're just observing a little more closely," the supervisor said.
Customs Service spokesman Patrick Jones said, "At a port like Buffalo, there's a percentage of inspectors that do chiefly administrative work. We'll be putting them on the lines."
He said in other parts of the country, inspectors are being transferred in from other locations to assist at little-used crossings, but that is not the case in Buffalo, Niagara Falls or Lewiston.
Jones said, "We are taking every precaution to protect people from dangerous people and dangerous things." He said the heightened state of alert will continue until intelligence agencies decide the increased terrorist threat is no longer evident.
U.S. authorities are still working to locate an alleged accomplice of Ressam, who apparently had been with him at a motel in British Columbia for three weeks before Ressam entered the United States.
Newsweek magazine reports Ressam is tied to the Montreal cell of an Algerian radical group. A Montreal police spokesman said Sunday that the link was a rumor not yet confirmed.
The spokesman, Andre Poirier, said Sunday that a massive manhunt was under way in Canada and the United States for the suspected accomplice. "He might be returning to Vancouver," Poirier said. "He might be in Seattle. We don't know."
Ressam reportedly had two ferry ticket stubs in his possession -- suggesting a companion may have walked off the boat -- when he was arrested in Port Angeles, a port city of 20,000 about 60 miles northwest of Seattle.
The FBI will not confirm that another man is being sought or otherwise comment on the case, Seattle spokeswoman Roberta Burroughs said.
News Niagara Bureau Reporter Thomas J. Prohaska contributed to this report.