The troops had been responding to unrest between the Okuama and Okoloba communities in the oil-rich southern Delta state.

"The cowardly offenders responsible for this heinous crime will not go unpunished," President Bola Ahmed Tinubu said, paying homage to the soldiers' sacrifice.

"The Defence Headquarters and Chief of Defence Staff have been granted full authority to bring to justice anybody found to have been responsible for this unconscionable crime against the Nigerian people," Tinubu added.

Tinubu said one civilian was also killed in what he termed "a direct attack on our nation".

Nigeria's military said Saturday the soldiers were killed in the Bomadi region on Thursday after being surrounded by local youths, during a bid to mediate between the ethnic Urhobo village of Okuama, and ethnic Ijaw from the neighbouring village of Okoloba.

Brigadier General Tukur Gusau said troops had "responded to a distress call", with media reports claiming the rival communities have clashed repeatedly over land ownership and fishing rights in recent weeks, leaving several people dead.

Gusau said an investigation was underway and several arrests had been made.

Okoloba village elder Clement Koki told AFP Okuama youths and "mercenaries" had posed a persistent threat for some months.

One Okuama resident, speaking on condition of anonymity, told AFP the army had lied about events and said "most of the soldiers presumed dead are Okoloba in military uniform" who he claimed had "opened fire" on his village, drawing an armed riposte.

Femi Falana, a lawyer and human rights campaigner, urged the military to resist any temptation to subject either of the two communities to a "retaliatory" attack.

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