Customs agents at six U.S. airports are being asked to look out for travelers from Pakistan with indications that they might have been to terrorist training camps in that country.

Homeland Security Department (search) official, speaking on condition of anonymity, said Tuesday that the agents were told to look for such physical evidence as rope burns, unusual bruises, wounds and scars — things that indicated recent participation in paramilitary training.

"There is no hard intelligence connecting the camps to a threat against the United States," the official said.

"It's not unusual to have specific information to assist our inspectors. This is part of our process," the official said, calling the notice a "regular border enforcement tool."

The notice, first reported by "CBS Evening News," was sent to customs inspectors at Newark Liberty International Airport, Washington's Dulles International Airport, New York's John F. Kennedy International Airport, Detroit Metropolitan Wayne County Airport, Chicago's O'Hare International Airport and Los Angeles International Airport.

Separately, government background checks of foreign airline crew members and truckers licensed to haul hazardous materials in the United States turned up 38 with possible terrorist connections, Homeland Security Department officials said Tuesday.

Asa Hutchinson (search), undersecretary for border and transportation security, said the agency reviewed the backgrounds of all 450,000 foreign crew members that flew into the country since March and identified nine pilots with potential ties to terrorists.

The Federal Aviation Administration (search) has barred all nine from flying into the country, he said. He declined to provide any individual information about the nine or to describe their links to terrorists.

Two additional flight crew members were found to have fraudulent passports and another had a criminal record of assault on a law enforcement officer. They are not permitted to fly in the United States, Homeland Security spokesman Dennis Murphy said.

Since 2002, a handful of other foreign pilots were barred from flying into the United States because of alleged terrorist connections. Hutchinson said the latest background checks were more thorough than those that turned up those pilots.

"This reflects a new capability of the Department of Homeland Security," Hutchinson said.

Homeland Security also looked into the backgrounds of 2.7 million truck drivers licensed to carry hazardous materials, Murphy said. Of those, 29 had possible relationships with terrorist organizations and are being investigated further, he said.

He declined to provide further details.