LAGOS, Nigeria (AP) - Nigerian President Olusegun Obasanjo on Tuesday ordered tighter application of safety and maintenance procedures for all Nigerian aircraft and promised an exhaustive probe into the cause of a weekend plane crash that killed all 117 onboard.

Making his first public appearance since the late-Saturday accident and death of his wife only hours afterward, a sombre-looking Obasanjo told Nigeria in a televised broadcast that he rued the pair of "tragic events."

"I have already ordered a full and thorough investigation into the cause of the air crash with a view to ensuring that this sort of calamity does not repeat itself," said Obasanjo.

"In addition, I have directed the aviation ministry to ensure strict compliance with maintenance and operational requirements and standards for all aircraft in order to plug loopholes and ensure passenger safety," he said.

The Bellview Airlines Boeing 737-200 had just left the airport at Lagos, Nigeria's biggest city, for the capital, Abuja, when it crashed near Lissa, about 50 kilometres north of the Lagos airport.

The crash carved a deep pit into the earth where investigators believe a large part of the aircraft and many bodies are still buried.

On Monday, 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.

Aviation Minister Babalola Borishade told reporters on Monday 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.

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

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.

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. Airline officials said 117 people were on board - 111 passengers and six crew members.

The nationalities of all those aboard were not immediately known, but most were believed to be Nigerians.

A U.S. army major assigned to the Office of Defence Co-operation at the U.S. Embassy in Nigeria was among them, U.S. military officials said Tuesday. He was identified as Maj. Joseph Haydon, 40, of Fredericksburg, Va.

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