President Olusegun Obasanjo ordered increased security around Nigeria's pipelines after a gasoline conduit explosion killed up to 200 people, as rescue workers sought Saturday to finish burying the dead in mass graves.

Twenty-two charred bodies could be seen floating Saturday in mangrove swamps up to five miles from Ilado village in southwestern Nigeria, where gasoline gushing from the pipeline exploded Friday, killing 150-200 villagers scavenging for the fuel.

Obasanjo described the situation as "grave" and ordered an investigation into the cause of the blast, Radio Nigeria reported. Obasanjo, on a state visit to Indonesia, called for increased protection of the pipelines, the radio said.

Countrywatch: Nigeria

Oil-region militants have targeted pipelines and other petroleum-industry infrastructure in Africa's oil giant, cutting production by a quarter. But there was no sign that Friday's fire on a ruptured pipeline was sabotage.

Lagos State Health Commissioner Tola Kasali said rescue workers milling about at the blast site Saturday were to finish burying the dead after interring about 100 on Friday.

Only after all bodies had been buried in mass graves would a definitive death toll be given, he said. But a firm toll seemed increasingly unlikely considering the bodies seen floating Saturday in just one arm of the region's labyrinth waterways and creeks.

Kasali said Friday that bodies in the region could pose a health risk to Nigeria's main city of Lagos, about 30 miles to the west, necessitating the quick and anonymous burial for the dead.

"We're concerned that if we don't do that, we'll create a health emergency in Lagos since it happened by the shore and the water will just flow back into the city," he said.

The European Union offered condolences.

"The presidency of the European Union expresses its sincere condolences to the country's government and people," the EU presidency said in a statement, adding that its sympathies were with the families and friends of those who lost their lives.

The blaze took place far from the center of the fishing village of Ilado, and it was unclear if there were witnesses. Boatsmen said they heard an explosion before dawn and saw the glow of flames.

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

The impoverished people of Nigeria often tap pipelines, seeking fuel for cooking or resale on the black market. The highly volatile gasoline can ignite, incinerating those collecting it.

More than 1,000 people in Nigeria, Africa's oil giant, 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. Pipes carry the crude to refineries across the nation.

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. It was unlikely Friday's blast would affect exports.

Nigerian militants have blown up oil pipelines and kidnapped foreign oil workers to press their demands for local control of oil revenues by inhabitants of the oil-producing south, who feel cheated out of the wealth produced in their backyards. The militant groups have cut production by nearly a quarter in recent months.