Bayelsa state police spokesman Asinim Butswat said the incident happened on Friday.
“A tugboat, towing a barge with a combined team of policemen from the Nigerian Inland Waterways, Nigeria Security and Civil Defence Corp (NSCDC), and civilians on board was attacked by suspected sea pirates at Ekebiri Waterways,” he said.
“A reinforced team arrived shortly and rescued one policeman, three NSCDC personnel and four civilians,” he said.
“However, a policeman, one NSCDC personnel and a civilian were shot dead by the sea pirates, one policeman is still missing,” he said.
Other groups gave different reports on those killed in the ambush.
Area NSCDC head Desmond Agu told AFP two police and one paramilitary officer were killed while three other security personnel were injured in the attack.
An official of the Nigerian secret police who did not want to be named, said four security personnel were killed.
“The operatives were ambushed around Okoron community while on their way to the Tebidaba flow station which is operated by the Nigerian Agip Oil Company (NAOC),” he told AFP.
Locals said there was a gunfight between the attackers and the security agents.
“We heard a series of sporadic gunshot at about 7:00 pm on Friday night,” Preye Fubara, a resident of Okoron community said.
“The corpses of the slain security operatives have been recovered without their rifles.”
No group has claimed responsibility for the incident, but militants seeking a fairer share of Nigeria’s multi-billion-dollar oil wealth stepped up their violent attacks on oil infrastructure last year, slashing output and hurting government revenue.
A government truce with the oil rebels has halted the attacks, but sporadic incidents against security personnel guarding oil installations persist in the region.