Four guards have been killed by gunmen at a facility operated by the Nigerian subsidiary of Eni, according to officials.
The members of the Nigeria Security and Civil Defence Corps (NSCDC), a paramilitary agency of the government, were killed on Monday at the installation close to the oil hub of Port Harcourt.
A spokesman for the NSCDC said the guards were shot dead by gunmen in camouflage.
There has been no immediate claim of responsibility.
A number of militant groups have carried out attacks in Nigeria including the Niger Delta Avengers on facilities owned by Shell, Chevron, Exxon and Eni.
The attacks have reduced Nigeria’s oil output and hammered government revenue amid low oil prices.