Nigerian militants ambushed a police boat in the oil-producing Niger Delta region over the weekend, and 12 policemen are missing from the boat, police said on Sunday.
Police Commissioner Kingsley Omire said the boat carrying 50 police officials was headed to a funeral late on Friday when it developed engine problems in one of the winding creaks of swampy delta region, home to Africa's biggest oil industry.
"The craft ... was a soft target for some hoodlums, who we have confirmed were part of a militant group that was supposed to be enjoying an amnesty," he said.
A Nigerian security source, who could not be named, said the 12 were very likely all dead.
Attacks in the restive Niger Delta region have been fewer since an amnesty for militants in 2009, although kidnapping, piracy, large-scale oil theft and pipeline sabotage still occur.
Omire said police believed the attackers to be a faction of a militant group that was disgruntled over not receiving a share of the amnesty money.
The Movement for the Emancipation of the Niger Delta (MEND), the main militant group prior to the amnesty, threatened in an email statement this week to restart attacks, in response to the jailing of its leader Henry Okah by a South African court.
Omire said this attack had nothing to do with MEND.
Okah was condemned to 24 years in prison on March 26 this year for masterminding two deadly car bombings in the Nigerian capital in 2010 that killed at least 10 people.
MEND has been largely inactive since most of its militants agreed an amnesty with the government in 2009, ending a wave of violence that at one stage cut oil production down by half.
A resurgence of militant activity would be a blow to President Goodluck Jonathan, himself from the same Ijaw ethnic group as most of the militants, and who helped negotiate the amnesty. His administration's security forces are already stretched by an Islamist insurgency in the north.