Nigerian militants have ambushed a police boat in the oil-producing Niger Delta region, killing 12 police officers, authorities said yesterday.

A resurgence of militant activity would be a major problem for multinational energy companies

The Movement for the Emancipation of the Niger Delta (Mend), the main delta militant group before a 2009 amnesty, claimed responsibility for Friday’s attack, staged shortly after it had threatened to resume its campaign of violence.

However, another of the armed groups roaming Africa’s top oil producer said it had carried out the ambush near the village of Azuzama, which a further 38 police officers survived.

Mend, whose activities at their peak cut oil production in Nigeria by around half before the amnesty, threatened to restart attacks this week in retaliation for the jailing of its leader Henry Okah by a South African court.

Mend said it had attacked the boat heading to a funeral in Bayelsa state because government forces had refused to take its threat seriously.

“For dismissing (our statement) ... as an ‘empty threat’, heavily armed fighters from ... Mend intercepted and engaged government security forces in a fierce gunfight at Azuzama,” said an emailed statement signed by Jomo Gbomo, a pseudonym the group uses.

“All oil companies and the public are advised to ignore the false sense of security being peddled,” it said, maintaining that the attack had been on Saturday, rather than Friday.

Bayelsa state Governor Henry Dickson confirmed the 12 policemen were dead, calling the incident “most tragic, shocking and disheartening”.

A resurgence of militant activity would be a blow to President Goodluck Jonathan, who helped to negotiate the amnesty and who is from the same Ijaw ethnic group as most of the militants. His administration’s security forces are already stretched by an Islamist insurgency in the north.

It would also be a major problem for multinational energy companies such as leading operator Royal Dutch Shell, already contending with industrial scale oil theft by armed gangs that saps up to a fifth of Nigeria’s two million barrel-a-day output, according to some Government estimates.

Police Commissioner Kingsley Omire said the ambush was actually carried out by militants once loyal to Kile Selky Torughedi, who headed Mend’s southern wing.