LISSA, Nigeria -- Nigeria said Monday it had requested help from the United States to determine what caused an airliner to slam into the bush, killing all 117 people aboard and carving a pit deep into the earth.
Aviation Minister Babalola Borishad did not rule out foul play as the reason why the Bellview Airlines Boeing 737-200 went down late Saturday north of Lagos, but said: "For now, we just believe it's an accident."
Earlier, the National Civil Aviation Authority chief 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," Fidelis 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.
Borishad said Nigeria had made a formal request for help from U.S. aviation investigators and forensic experts. U.S. Embassy officials had no immediate comment.
The flight lost contact with the control tower five minutes after taking off from the Murtala Muhammed International Airport in Lagos en route to the capital, Abuja, officials said. State radio said its pilots issued a distress call before the plane disappeared from the radar.
It crashed near Lissa, about 30 miles north of the airport in Lagos, Nigeria's largest city. It was to be a 50-minute flight.
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.
Ayeni said residents 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 25-foot-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.
Nigeria announced a three-day, nationwide mourning period for victims.
Small bits of fuselage, human flesh and clothing were strewn in a nearby copse of trees. No identifiable bodies could be seen.
Ogo Odingbesearched 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'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 before authorities had made a full assessment of the situation.
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.
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.