A helicopter travelling between oil facilities in Nigeria operated by Italy's Agip was hit by gunfire on Wednesday, wounding one passenger, but the aircraft landed safely.

The Sikorsky 76 was flying between the Ogbainbiri and Tebidaba oil flow stations operated by Agip when it was hit, according to Lieutenant-Colonel Nkana Efik, commander of the military taskforce in the southern state of Bayelsa.

Efik said the helicopter appeared to have been hit by a single shot. It was not clear who fired it.

"One passenger was wounded but the aircraft safely returned to its base in Port Harcourt," Aerocontractors, the company operating the helicopter, said in a statement.

"The injured party is now receiving hospital treatment and the helicopter is undergoing appropriate checks from Aero's maintenance team," it said, adding that further flights to the area had been suspended while the authorities investigated.

The Niger Delta, a network of mangrove creeks which is home to Africa's biggest oil and gas industry, has been plagued by pipeline bombings and the kidnapping of oil workers. Attacks on helicopters are not unprecedented but are comparatively rare.

The Tebidaba flow station and its pipelines, which ship crude oil to the Brass River export terminal, have been attacked several times over the past few years.

The Movement for the Emancipation of the Niger Delta (MEND), the region's main militant group, warned this month of attacks on Italian firms including Agip because of what it said was an Italian offer to supply two attack boats to the military.

Italy said it had offered cooperation and assistance to the Nigerian government in fighting drug trafficking and crime but that there had been no specific offer of military vessels.

Nigerian security forces repelled an attack by gunmen on Agip's Twon Brass oil terminal, also in Bayelsa, on Saturday night. Oil production at the facility was not affected.