No group has claimed responsibility for the attack, according to a senior police officer. Security agents are investigating the incident.

Oil pipelines, facilities and personnel of oil majors operating in Nigeria's restive oil-rich Niger Delta have been targets of violent attacks in the past three years. 

The oil giant Shell said on Friday that it had contained a spill caused by sabotage on its Adibawa delivery line in the southern Bayelsa state. Last week, armed men attacked Chevron's Robert-Kiri flowstation, killing a Nigerian navyman.

Since January 2006, attacks have cut Nigeria's oil output by more than one quarter. Nigeria's total production currently stands at around two million barrels a day against 2.6 million barrels in 2006.