The pilot on a Virgin Atlantic flight that spent several hours on the tarmac after being diverted to Connecticut had asked for permission to let the passengers get off the plane, but a customs official threatened to have them arrested if they did, the airline said Thursday.

Customs officials denied the airline's allegation.

The trans-Atlantic flight's captain was told by a customs official at Bradley International Airport in Windsor Locks that passengers couldn't get off the plane until more immigration officials arrived, Greg Dawson, an airline spokesman in London, said in an e-mail to The Associated Press. It took more than two hours for the officials to arrive, he said.

Storms diverted the London-to-Newark, N.J., flight. Passengers sat on the tarmac in Connecticut for four hours beginning around 8:30 p.m. Tuesday into early Wednesday in rising heat and darkness. Travelers said they were offered water but no food; some fainted.

A federal rule limiting tarmac time to three hours does not apply to international flights.

U.S. Customs and Border Protection did not receive a call from the pilot, and no one from the agency refused a request to allow passengers off the plane, said Theodore Woo, an agency spokesman in Boston.

Customs officers headed for the airport "as soon as we got the call at 11 p.m.," Woo said. At that point, customs had enough officers to "escort passengers to a safe area," he said.

Airport officials have said there was only one customs official at the airport Tuesday night when the flight arrived in Connecticut.

"That's outrageous. If it's true, it's unacceptable," passenger rights advocate Kate Hanni said of Virgin Atlantic's allegation. She said she expects U.S. Transportation Department officials to listen to any audio recordings made of conversations between pilots and customs officials to verify the allegation.

Transportation officials declined to comment during an investigation.

Last year, the agency's investigation of an overnight stranding of Continental Express passengers on a runway in Rochester, Minn., revealed the flight's captain requested passengers be allowed entrance to the closed airport terminal.

An employee of another airline _ the only person still working inside the terminal _ refused to open a gate. Audio recordings showed the employee cited the absence of Transportation Security Administration workers in turning down the request.

The Transportation Department should consider including Customs and Border Patrol and the TSA in future regulations related to tarmac strandings, Hanni said.

"They appear to be a roadblock," said Hanni, founder of Flyersrights.org. "Often airlines tell us customs or TSA refused to allow passengers off planes."

Two years ago, the TSA told a task force on tarmac strandings that the agency wouldn't object to passengers being deplaned if they could be contained in a secure room inside the airport, Hanni said.

The airport called for customs inspectors around 11 p.m. when it learned the Virgin flight was canceled, said John Wallace, a Bradley spokesman. Passengers were allowed off the plane about an hour and 15 minutes later, when customs officials arrived, he said.

Bradley's only regular international passenger flights are to Canada, and it does not house many customs agents, Wallace said.

Connecticut Transportation Commissioner Joseph F. Marie disputed a comment Wednesday by a Virgin spokeswoman in London that Bradley, which is operated by his agency, "isn't used to dealing with international flights."

Bradley has handled 47 diversions of international flights in the last 12 months "without incident until this one," Marie said.

Virgin Atlantic said in an e-mail that it will not comment until it gathers information about the incident.

Marie said he will contact Virgin, the Federal Aviation Administration and Customs to investigate.

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Associated Press writer Joan Lowy in Washington contributed to this report.