Authorities were searching for a man who walked through a screening checkpoint exit into the secure side of a terminal on Sunday night at a U.S. airport, and flights were grounded and passengers being re-screened, an air safety official said.

A man was seen at Newark Liberty International Airport walking down an exit lane at Terminal C, said Transportation Security Administration spokeswoman Ann Davis. Screening was halted in the Continental terminal while authorities looked at surveillance tapes to identify the man.

Passengers were then evacuated from the secure side of the terminal and moved to the open side to go through screening again to ensure that every passenger boarding a plane out of the terminal was fully screened, Davis said in a statement. The security line was emptied, and passengers were waiting in check-in areas.

No announcements had been made over the airport's public-address system as of 9:45 p.m. Security officers were instructing passengers, who were expressing frustration over the situation.

Alison Day, 47, of York, England, was supposed to leave for Manchester, England, at 7:30 on Sunday night. She was traveling with a party of seven including an 18-month-old and 5-year-old.

``I'm not angry that this is happening, but I'm angry that there was a lack of organisation,'' she said.

She said her party, headed home after a Caribbean cruise, was escorted out of Continental's lounge but given no further instructions.

Continental spokeswoman Susannah Thurston said it's an airport security issue not involving the Houston-based airline.

A spokesman said the Port Authority of New York and New Jersey is assisting with the possible security breach, and Davis had no update late Sunday night on the man who walked through the exit.

Also on Sunday, the Transportation Security Administration said passengers flying into the United States from nations regarded as state sponsors of terrorism and ``countries of interest'' will be subject to enhanced screening techniques, such as body scans and pat-downs.

Starting on Monday, all passengers on U.S.-bound international flights will be subject to random screening.

The State Department lists Cuba, Iran, Sudan and Syria as state sponsors of terrorism. The other countries whose passengers will face enhanced screening include Afghanistan, Algeria, Iraq, Lebanon, Libya, Nigeria, Pakistan, Saudi Arabia, Somalia and Yemen.

Umar Farouk Abdulmutallab, the Nigerian man who allegedly tried to set off an explosive device aboard a Northwest airliner on Christmas Day, has told U.S. investigators he received training and instructions from al-Qaida operatives in Yemen.

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