PHILADELPHIA, Pennsylvania (USA) - A company hired criminals to man security checkpoints at Philadelphia International Airport even after being fined last year for inadequately checking employees' backgrounds, prosecutors said Thursday.

Argenbright Security Inc. of Atlanta pleaded guilty to violating federal rules on training, testing, and conducting background checks on employees. It paid a $1 million fine, was placed on probation for three years, and agreed to conduct background checks on employees nationwide.

A motion filed Thursday accused Argenbright of still not checking backgrounds adequately. U.S. Attorney Patrick Meehan said he is seeking new sanctions against Argenbright, including an order that the company regularly audit its work force and fingerprint all employees.

Prosecutors said inspections in the past year found 18 guards with convictions ranging from drug possession to burglary and resisting arrest.

Argenbright President Bill Barbour said the company is willing to make the changes, including fingerprinting employees.

``We generally embrace the remedies that have been recommended to the court,'' he said.

Meehan said inspectors also found the company failed to do adequate background checks of employees in 13 other airports. Argenbright provides security at most of the biggest airports in the United States.

Barbour disputed the allegation that the problems are widespread, saying an audit by the Federal Aviation Administration completed in July found ``very few discrepancies'' in the company's training and screening techniques.

Argenbright handles passenger checkpoints, baggage, and other services for American and United airlines at Dulles International Airport near Washington and Newark International Airport in New Jersey. Two of the planes hijacked Sept. 11 had departed from those airports.

The company also provides services at Boston's Logan Airport, but does not work for United or American, the airlines whose planes were hijacked there and crashed into the World Trade Center.

Meehan said the investigation was ongoing and the court filing is ``not directly related'' to attempts to tighten airport security nationwide.

``Issues like this deserve attention at any time, although I believe the scrutiny and response will be heightened because of the recent horrific events,'' he said.

In response to Thursday's filing, U.S. Secretary of Transportation Norman Mineta announced he was assigning a special enforcement team to Philadelphia International Airport to ensure that security officers get thorough background checks before they are hired. The team was to be made up of a federal security manager from the FAA and agents from the Department of Transportation.