PORT HARCOURT, Nigeria (AP) _ Dozens of militants sank two military patrol boats in Nigeria's oil-rich, southern delta Monday in an attack that killed five soldiers and left nine others missing, an army spokesman said.

Maj. Sagir Musa said 15 soldiers were on a routine boat patrol in a delta outlet when 70 militants attacked, sinking two military boats. One of the soldiers managed to escape and raise the alarm, he said, giving the casualty toll.

Bisi Ojediran, a spokesman for Royal Dutch Shell PLC in Lagos, said a convoy belonging to the company was attacked Monday while accompanied by a military escort in the area Musa described.

It was not immediately clear if the two reports referred to the same incident, or if anyone was taken captive. Ojediran said he could not confirm any casualties.

A group that says it represents a coalition of militant groups claimed responsibility for attacking the Nigerian soldiers. An e-mail from the Joint Revolutionary Council said the attack was in revenge for attacks on local communities and demanded the release of imprisoned militant leader Mujahid Dokubo-Asari.

However, an e-mail from the Movement for the Emancipation of the Niger Delta, one of the groups the coalition claims to represent, said it was not involved in Monday's violence.

Kidnappings and attacks on oil facilities have become common in the West African country's southern delta. Militants argue that residents remain impoverished and benefit little from the country's vast oil wealth while government officials and oil companies grow rich.

Attacks have cut Nigeria's daily oil production by nearly a quarter from its normal 2.6 million barrels. The country is Africa's biggest oil exporter and the fifth-largest supplier of crude oil to the United States.