Rescue workers said Sunday that they have buried the bodies of at least 165 people killed in a pipeline explosion in southern Nigeria, but others remain uncollected, raising fears of a health risk.

Up to 200 people died in the inferno that erupted when the pipeline burst in the village of Ilado, igniting the fuel, local officials said. Boatsmen said they heard an explosion and saw the flames erupt before dawn Friday.

President Olusegun Obasanjo, calling the situation "grave," ordered better protection of Nigeria's vast network of pipelines and an investigation into what caused the inferno, Radio Nigeria reported Saturday.

Obasanjo's order for greater security around the pipelines comes as militants step up attacks on pipelines and other petroleum-industry infrastructure in Nigeria, Africa's leading crude producer that have cut production by a quarter and have sent crude prices soaring on international markets.

But many Nigerians said they doubted it was an attack. They say impoverished villagers regularly tap the pipes to pilfer fuel, drawn by the allure of free fuel for cooking or resale on the black market, and are undeterred by the danger of a deadly explosion.

"This has been going on for a long time; those people were just unlucky they caught fire this time," said Hakim Bolaji, 32, a boat driver who plies the swamps.

"People are making so much money from selling stolen petrol that I'm sure they'll come back," he said.

Rescue gathered and interred dozens of bodies and sprayed disinfectant at the blast site Saturday, Lagos State Health Commissioner Tola Kasali said. More than 100 bodies were buried Friday and at least 65 on Saturday, according to police counts.

But a definitive death toll will be released only after all the bodies are buried in a mass grave, he said. A firm toll seemed increasingly unlikely; at least four bodies could be seen floating in tidal mangrove swamps as far away as a few 5 kilometers (3 miles) from the blast site.

Kasali said the bodies could pose a health risk to Lagos, which lies about 50 kilometers (30 miles) to the west, necessitating the quick and anonymous burial for the dead. A labyrinth of waterways and creeks lead to a network of lagoons that surrounds Lagos, Nigeria's biggest city.

The pipeline is run by Nigeria's state oil company and was used to transport gasoline across the country for national consumption.

Countrywatch: Nigeria

More than 1,000 people in Nigeria have died in recent years when fuel they were pilfering from pipelines caught fire.

In 2004, a pipeline exploded near Lagos as thieves tried to siphon fuel, killing as many as 50 people. A 1998 pipeline blast killed more than 700 in southern Nigeria.

Most of Nigeria's oil is pumped in the southern Niger Delta region, far from Lagos. Nigeria, which normally pumps 2.5 million barrels of crude per day, is Africa's largest producer and the fifth-largest source of imports to the United States.

Despite Nigeria's rich natural resources, most of the country's 130 million people are very poor. This inequity, blamed on official corruption or mismanagement, is what motivates the militants behind the attacks as well as the villagers' theft of fuel they view as their birthright.