Militant attacks have sharply cut Nigeria's oil output
The main militant group in Nigeria's Niger Delta says it has attacked an oil facility, the second attack since a government amnesty offer last Thursday.
Royal Dutch Shell said it was stopping some production as a precaution after reports of an attack on two oil well clusters near its Forcados terminal.
The militants said the facility was on fire after the early morning attack.
The army has denied militant claims that a gunboat with soldiers on board was sunk during the raid.
Military spokesman Lt Col Rabe Abubakar said the Joint Task Force was sticking to the terms of the amnesty and would not attack militants unless fired upon.
The amnesty for militants is a bid to end years of crippling attacks, which have sharply cut oil production.
Some of the militant groups which operate in the Niger Delta's lawless swamps have agreed to disarm, on condition that they meet the president to iron out various issues.
The main group - the Movement for the Emancipation of the Niger Delta (Mend) - has said it will not disarm until militant leader Henry Okah is freed from jail.
He is facing trial on charges of gun-running and treason after being arrested in Angola in 2007.
On Friday, the government offered to free him - but only if Angola agrees.
Before the amnesty, a JTF operation was under way in Delta State to hunt down Mend fighters which had forced thousands of people to flee their homes.
The militants claim they are fighting so local people benefit more from their region's oil wealth.
But many attacks are undertaken for financial gain and they have reduced oil production to 1.3m barrels per day, officials say. Nigeria's Opec quota is 2m.