Nigeria said Monday it had requested expert help from the United States to determine what brought down a passenger jet, whose crash carved a deep pit into the earth and killed all 117 aboard.

Aviation Minister Babalola Borishade told reporters at the crash site his country had made a formal request to the United States for aviation investigators and forensic experts. He did not completely rule out the possibility of foul play, but said, "For now, we just believe it's an accident."

Earlier, Fidelis Onyenyiri, chief of the National Civil Aviation Authority, had said a "natural cause" was likely.

"The weather was not too bad but there was lightning, and an airplane struck by lightning could lose total control," Onyenyiri said. "There were signs of disintegration which could be caused by impact or other means. Our preliminary position is that the airplane seems to have lost control and went down.

Lightning has rarely been confirmed as the cause of a crash.

The Bellview Airlines Boeing 737-200 had been on the way from Lagos, Nigeria's biggest city, to its capital, Abuja, when it crashed late Saturday near Lissa, about 30 miles north of the Lagos airport.

One area resident, Lanre Ayeni, said he believed the plane may have exploded before falling to the ground. His account couldn't be verified.

"We heard a loud bang in the sky and then saw a large ball of fire fall down, followed by a massive explosion and more fire," said the 30-year-old carpenter.

Most Lissa residents were fearful and only approached the crash site hours later, after dawn, he said.

Ayeni said they found a scene of smoldering devastation, with aircraft parts and clothes hanging in trees and no sign of life.

Acrid smoke still curled from an eight-meter deep pit Monday as investigators picked through nearby wreckage, looking for flight-data recorders - the so-called black boxes, which are actually often blazing orange for easier identification.

Small bits of fuselage, human flesh and clothing were strewn in a nearby copse of trees. A hand and leg lay on the ground. No identifiable bodies could be seen but the smell of death hung close.

Ogo Odingbe wailed and searched the site Monday for signs of her brother, who was aboard the flight.

"I can't even find his clothes or anything to identify him. How can he go without a trace?" cried the 28-year-old.

Nigeria announced a three-day, nationwide mourning period for victims.

Nigeria's Broadcasting Commission lifted the temporary closure of two broadcasters for what it termed "gross unprofessional conduct" in airing grisly crash-site footage and reporting that no one survived the crash before authorities had made a full assessment of the situation or notified victims' families.

After protests by Nigerians, the agency said it was treating the matter with "some measure of magnanimity" in only issuing a warning that any other such breaches will be sanctioned.

There was much official confusion on Sunday, with regional and local officials giving erroneous reports on whether there were survivors - or even where the crash had occurred. Federal officials gave little information until late in the day.

Military helicopters first spotted the smoldering wreckage of the Nigerian-run Bellview jet on Sunday, and search teams that visited the site afterward found no survivors, said Onyenyiri, chief of the National Civil Aviation Authority.

Initial reports indicated the plane lost contact with the Lagos control tower five minutes after taking off from Murtala Muhammed International Airport in Lagos at 8:45 p.m. on Saturday and state radio said pilots issued a distress call before the plane disappeared from radar.

The 50-minute flight to Abuja was a popular route among Nigerians and expatriates.

The nationalities of those aboard were not immediately known, but most were believed to be Nigerians. Airline officials said 117 people were on board - 111 passengers and six crew members.

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