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(CNN) -- -- A poor decision by a regional airline was being blamed Friday for Continental Airlines passengers getting stranded overnight as their plane sat on a tarmac in Minnesota, federal transportation officials said Friday.

Passengers on a Continental flight operated by ExpressJet sat on the tarmac for nearly six hours on August 8.

U.S. Transportation Secretary Ray LaHood said a representative of Mesaba Airlines improperly refused requests by the plane's captain and crew to let passengers off the plane. They were stuck on the tarmac in Rochester on August 8 from 12:38 a.m. to about 6 a.m. with nothing but pretzels to eat, LaHood said.

"There was a complete lack of common sense here," LaHood said in a written statement. "It's no wonder the flying public is so angry and frustrated."

Mesaba, based in Eagan, Minnesota and owned by Delta Air Lines, was the only carrier able to assist Continental Flight 2816, which was on its way from Houston, Texas, to Minneapolis, Minnesota, when it was diverted because of strong thunderstorms, LaHood said.

The flight's 47 passengers described crying babies, overflowing toilets and cramped conditions.

According to a Department of Transportation preliminary report, Mesaba's representative refused to help passengers off of the plane, incorrectly saying the airport was closed to passengers for security reasons.

LaHood, who called the incident a "nightmare," said federal regulations allow passengers to get off of a plane, enter an airport and reboard without being screened by safety personnel as long as they remain in a secure part of the terminal.

Mesaba said Friday that its employees tried to help.

"Mesaba respectfully disagrees with the DOT's preliminary findings as they are incongruent with our initial internal review of the incident," CEO John Spanjers said in a written statement. "Because Continental Express Flight 2816 diverted to an airport where they have no ground handling service, Mesaba offered assistance as a courtesy during this delay.

"While the investigation is ongoing, Mesaba is fully cooperating with the Department of Transportation and looks forward to the final report."

Mesaba is a wholly owned subsidiary of Northwest Airlines, which is a wholly owned subsidiary of Delta Air Lines.

Delta CEO Richard Anderson said the airline is working with Mesaba, Continental and the Department of Transportation to help determine exactly what happened.

In the department's statement, LaHood said that the Continental crew was not at fault for the passengers being stuck.

"In fact, the flight crew repeatedly tried to get permission to deplane the passengers at the airport or obtain a bus for them," he said.

Department of Transportation investigators have interviewed passengers, the flight crew, airport workers and others during an investigation expected to be completed in the next few weeks.

The department "is considering the appropriate action to take against Mesaba," according to the statement.

The investigation did show that while the crew of the flight, operated by carrier ExpressJet, did all it could, higher-level officials should have become involved in the effort.

The Aviation Enforcement Office has proposed regulations requiring airlines to have plans for how to handle lengthy tarmac delays.