Four members of the Nigeria Security and Civil Defence Corps, a paramilitary agency of the government, were killed on Monday at the installation at Omoku, near the oil hub of Port Harcourt, they said.
They were shot dead by gunmen in military camouflage, they said.
“The (security) operatives had engaged the gunmen in a fierce gun battle on realising that the intruders were not military men,” state NSCDC spokesman Michael Oguntuase told AFP.
A community leader in Omoku who did not want to be named, confirmed the incident.
“Dressed in camouflage, they came in a speed boat at about 6:40pm on Monday, exchanged gunfire with the operatives, leading to the death of four,” he said.
He said an unspecified number of NSCDC personnel were wounded.
Officials at Agip, the local subsidiary of Eni, were not immediately available for comment. There was no immediate claim of responsibility.
Since the start of the year, several militant groups, Including the Niger Delta Avengers (NDA), have bombed pipelines and facilities operated by oil companies, including Shell, Chevron, Exxon, Eni and state-run NNPC in the restive oil-producing south.
The attacks have slashed Nigeria’s oil output, hammering government revenue at a time of global low prices.
Nigeria is currently struggling to come out of a recession since August.
The attacks on oil infrastructure have continued despite government’s peace moves.