U.S. Transportation Secretary Ray LaHood on Friday blamed an employee at Delta Air Lines Inc. (DAL) for exacerbating a delay that left passengers stuck on a rival's jet at a Minnesota airport for almost six hours.

However, the chief executive of Mesaba Airlines, the Delta regional airline unit targeted by the secretary, said he disagreed with the DOT's initial findings.

LaHood said the initial probe into the incident revealed that an employee at Mesaba had been the only person at the airport in a position to help.

LaHood said in a statement that the Mesaba official had "improperly refused" a request from the plane's captain to allow passengers into the terminal.

The employee mistakenly believed that the Transportation Security Administration had to clear the late-night disembarkation, LaHood said. "There was really a complete lack of common sense here," he added.

"The Aviation Enforcement Office is considering appropriate action to take against Mesaba as it completes the investigation, which it expects to conclude within a few weeks," added LaHood, noting that senior staff at Continental and ExpressJet should have gotten involved earlier.

However, Mesaba CEO John Spanjers questioned the DOT's initial assessment.

"Mesaba respectfully disagrees with the DOT's preliminary findings as they are incongruent with our initial internal review of the incident," he said in a statement.

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."

LaHood had previously pointed the finger at ExpressJet Holdings Inc. (XJT), which operated a flight diverted by bad weather on behalf of Continental Airlines Inc. (CAL).

LaHood said the probe revealed that the ExpresJet flight crew were not at fault, and had made repeated efforts to get passengers into the airport terminal.

He had previously called on DOT officials to see whether ExpressJet and Continental had violated any laws in its handling of Houston-Minneapolis flight, diverted by bad weather to Rochester, Minn.

ExpressJet shares jumped after the announcement and closed at $2.68, up 69%. Continental shares ended up 8.4% at $13.05, while Delta finished 4.9% higher at $7.13.

Delta said it was working on an internal probe with Mesaba, and cooperating with DOT and Continental.

Continental and ExpressJet both reiterated an apology to the affected passengers and said they would work to avoid any recurrence.

LaHood's unusual public intervention comes as the DOT considers whether to require airlines to allow passengers off delayed planes within a specified period.

The incident has reawakened the debate over a long-mooted "passenger bill of rights" in the U.S. There are no mandatory requirements for airlines in handling flight delays. Some lawmakers are pushing for a three-hour limit before passengers must be allowed off a delayed aircraft.

-By Doug Cameron, Dow Jones Newswires; 312-750-4135; doug.cameron@dowjones.com