Nairobi/Malabo - Security forces in Equatorial Guinea have arrested 15 people in connection with an attack on the presidential palace, reports said Thursday.

Various media quoted the West African nation's state radio as saying that several other attackers had been killed or wounded.

A three-hour firefight broke out in the early hours of Tuesday morning when gunmen who arrived in the capital Malabo by boat launched their attack.

President Teodoro Obiang Nguema was not in the residence at the time. Obiang has ruled since seizing control in bloody coup in 1979.

Equatorial Guinea, the third-largest oil producer in sub-Saharan Africa, has undergone decades of instability.

British mercenary Simon Mann is currently serving a 34-year jail sentence in Malabo after being found guilty of leading a coup attempt in 2004.

However, the Spanish Ambassador in Malabo, Javier Sangro de Liniers, told national broadcast RNE that the attackers had no political goals and were merely criminals.

State media have accused Nigerian oil militant group the Movement for the Emancipation of the Niger Delta (MEND) of carrying out the attack.

MEND denies any involvement.

Malabo sits on the island of Bioko, about 200 kilometres from the Nigerian oil city Port Harcourt. (dpa)