"It's just to register Nigeria's place as a peacemaking country, a country that delights in peace and tranquility, not only for itself but for its neighbours," said Remi Oyo, spokeswoman for President Olusegun Obasanjo.

The ship was deployed from Nigeria's southeastern port of Calabar last weekend and is now patrolling off Bioko, Equatorial Guinea's main offshore island and the seat of its capital Malabo, according to reports in Nigeria.

Last week, the government of Equatorial Guinea's President Teodoro Obiang Nguema arrested 15 foreign nationals and accused them of being mercenaries and of planning to launch a coup d'etat in favour of an exiled opposition leader.

At the same time, Equatorial Guinean security forces began a sweep to round up suspected illegal immigrants, expelling hundreds of west and central Africans. More than 100 Nigerians took refuge in their embassy.

But Oyo emphasised that Nigeria remains a friend to its near neighbour, which lies just 100 kilometres (62 miles) off its southern coast. Both countries have significant oil fields under the Gulf of Guinea.

"Equatorial Guinea remains a close ally of Equatorial Guinea," she said.

"If there's a threat to peace anywhere, there's a threat to peace in Nigeria, there's a threat to peace in west Africa," she added.

Asked if Obiang's government had requested the deployment, she said simply: "Our ship is there and Equatorial Guinea is not against it."

Nigeria has west Africa's most powerful military, and has been the backbone of international peacekeeping missions in Liberia and Sierra Leone, but has a limited naval strength based around four former World War II US patrol ships.

WAR.WIRE