WASHINGTON – Army criminal investigators are looking into damage to two military helicopters on a production line at a Boeing Co. plant in suburban Philadelphia, prompting the company to shut down the line.

Rep. Joe Sestak, a Democrat whose district includes the plant, said Wednesday he was told that wires that appeared to be broken or severed were found in one helicopter and a suspicious washer was found in a second.

There is a “low probability that it was not deliberate,” Sestak said, but he added that unintentional damage remains a possibility. Sestak said he has communicated with company and union officials at the plant and was told the investigation could take two weeks.

The company didn't disclose specifics about why it shut down the H-47 Chinook line Tuesday at the Boeing Rotorcraft Systems plant in Ridley Township, Pa. Employees reported to work Wednesday morning, but the line had yet to fully resume operations.

Dave Foster, an Army spokesman, said in an e-mail that normal production was expected to resume shortly.

“At present, this is thought to be an isolated incident, confined to these two aircraft,” Foster said.

Foster said the Defense Contract Management Agency was overseeing the situation.

All aircraft at the plant were being inspected, said Jack Satterfield, a company spokesman. He said the shutdown was isolated to one line at the plant and did not affect helicopters already in use by the military.

The Defense Criminal Investigative Service had agents on the premises conducting interviews, said Gary Comerford, a spokesman for the agency. Army Criminal Investigation Command spokesman Christopher Grey confirmed the agency was also involved in the investigation, but said he could not comment on it.

The Chinook is known as the Army's workhorse aircraft. It is used to transport troops and supplies.

Boeing is currently producing new Chinooks for the Army, as well as updating older models.