The attack highlights the vulnerability of Nigeria's oil infrastructure
US oil giant Chevron has halted onshore oil production at its Escravos oilfield after an attack on a pipeline.
The loss could equate to about 120,000 barrels per day, about 6.6% of Nigeria's total daily crude production.
The Nigerian military said militants blew up the Niger Delta pipeline, but the region's main armed group blamed angry youths for the attack.
Earlier this week, Nigeria's president ordered tighter security in the Delta after an attack at a Shell facility.
According to the BBC's Alex Last, in Lagos, sources in the western Niger Delta believe the latest attack is the work of illegal oil "bunkerers" - involved in the lucrative trade in stolen oil.
The earlier attack on Shell's floating oil platform at Bonga, which cut a tenth of Nigerian oil production in one go, was carried out by militant group the Movement for the Emancipation of the Niger Delta (Mend).
News agencies quoted Mend as saying that it was not responsible for the Escravos incident, which occurred on Thursday night.
Mend said it had been contacted by angry youths who reported having blown up the pipeline, the Associated Press said.
The Escravos incident highlights the vulnerability of the oil infrastructure in Nigeria, our correspondent says.
With the government planning to hold a big summit of Niger Delta leaders and more money expected to flow to the Niger Delta, perhaps the armed groups there feel it is a good time to show how relevant they are to any chance of peace, our correspondent adds.
While the loss to Nigerian crude output is significant, it is a small fraction of the daily global oil output, of about 85 million barrels per day.
News of the Escravos attack comes ahead of a meeting in Jeddah, Saudi Arabia, of major energy producers and users - where the rising price of oil will be the key topic for discussion.
On Friday the Nigerian government announced how it would spend a $10bn (£5bn) windfall from the rising oil price.
It will spend just over $5bn fixing the country's power supply and the rest will be shared among the 36 state governments.