PORTLAND, Maine — The Portland International Jetport’s passenger terminal was evacuated and outbound flights halted for 3½ hours Thursday after security screeners spotted a suspicious object in a man’s carry-on bag.

The object turned out to be harmless but authorities refused to say what it was.

The Portland Police Department bomb squad used a robot to remove the bag containing the suspicious device from an x-ray machine. The bag was then placed in a bombproof container, which was taken to the far end of the airfield for evaluation, said Paul Bradbury, airport manager.

After screening came to an abrupt stop at 10:39 a.m., passengers were ordered to leave the secure area and go downstairs to the far end of the first floor of the terminal. Screening by the Transportation Security Administration resumed at 2:18 p.m., said Ann Davis, a TSA spokeswoman in Boston.

Barbara Kenney, a frequent business traveler, told WCSH-TV in Portland that she was waiting in the security screening line when officials halted outbound flights. She saw a man being questioned by TSA officers before being led to another room.

Bradbury said the suspicious object turned out to be a standard item found in any checked luggage, but he said law enforcement officials did not want to identify it.

The Portland airport gained notoriety after the Sept. 11 attacks when it was learned that ringleader Mohamed Atta started his day there. He flew to Boston, where he boarded an American Airlines jetliner that he flew into the World Trade Center.