UPDATE 2-Gunmen attack Nigerian navy near Shell oil facility

(Adds details, background)

By Austin Ekeinde

PORT HARCOURT, Nigeria, Nov 21 (Reuters) - Gunmen attacked a Nigerian navy houseboat guarding a Royal Dutch Shell (RDSa.L) oil flow station on Friday, the second such strike in as many days in the western Niger Delta.

The attack at the Nembe Creek flow station in Bayelsa state took place at around 3 a.m. (0200 GMT), Rabe Abubakar, spokesman for the joint military task force in the western delta said. He said the Shell facility itself was not damaged.

"There is no report so far of any (deaths) but we are collecting more details," Abubakar said.

A security source in the oil industry said four naval personnel were wounded and three more were unaccounted for.

Shell referred enquiries on the attack to the authorities.

Attacks on oil facilities are frequent in the Niger Delta, a vast network of mangrove creeks opening into the Atlantic Ocean and home to Africa's biggest oil and gas industry.

Some are carried out by militants who say they are seeking a fairer share of the region's natural wealth, others by criminals seeking to protect a lucrative trade in stolen oil, known as "bunkering", or to settle scores with the military.

Local communities have sometimes tried to sabotage oil facilities to force the multinationals to pay them compensation for the resulting environmental damage, security experts say.

The organised militant campaign has focused largely on Rivers state in the eastern Niger Delta in recent months but there have been a growing number of violent incidents in Bayelsa and Delta states to the west.

The Movement for the Emancipation of the Niger Delta (MEND), the region's main militant group, has said it believes the military are preparing to raid militant camps in Bayelsa and Delta. It has threatened to end its ceasefire and resume attacks on the oil industry if provoked.

The military said it repelled an attack by gunmen in speedboats on Thursday close to the Escravos oil export terminal in Delta state, operated by U.S. energy giant Chevron (CVX.N).

A Chevron spokesman said operations were normal at the terminal and that no employees had been wounded.

An oil industry security source said that attack had been carried out by disgruntled members of the local Itsekiri community who wanted more recognition from Chevron.

In a separate incident on Sunday, gunmen hijacked the MV Thou Galaxy cargo ship and its crew as it sailed towards Warri in Delta state in apparent retaliation for the military's capture of a vessel used in oil bunkering.

The ship and its crew were released on Monday. (For full Reuters Africa coverage and to have your say on the top issues, visit: africa.reuters.com/ ) (Writing by Nick Tattersall; Editing by Elizabeth Piper)