"We shut down production at the Bonga oilfield following an attack by unknown militants this morning," Shell spokesman Precious Okolobo said.
Meanwhile in an earlier report, the most powerful militant group in Nigeria said it launched a rare attack on Thursday against an offshore oil rig but failed to cripple the installation.
A leader of the Movement for the Emancipation of the Niger Delta told The Associated Press that several open-hulled boats filled with militant fighters traveled through heavy seas to the Bonga oil field more than 65 miles (100 kilometers) from land and launched an attack against a rig there.
But the fighters weren’t able to enter a computer control room that they had hoped to destroy with the aim of shutting down all production from the oil field.
The militant leader spoke on condition of anonymity to avoid punishment by authorities. The account could not be immediately verified.
Officials for Royal Dutch Shell PLC, which is a main operator in that oil field, had no immediate comment.
The militants also said they kidnapped a foreign worker from a supply vessel ferrying crew and supplies in the area, but there was no immediate confirmation. Hostages are normally released unharmed after a ransom is paid.
Attacks against offshore facilities are exceedingly rare.
Oil industry officials consider their operations on the high seas much safer than those in the creeks and swamps of Nigeria’s southern Niger Delta, where most of the attacks during two years of increased violence have taken place.
Militant attacks on oil infrastructure have trimmed about a quarter of total oil production in Nigeria, which is Africa’s biggest producer and a member of Opec.
The turmoil in Nigeria’s south has helped send oil prices to historical heights, which gives the militants more leverage in their drive to force the federal government to send more oil-industry proceeds to their areas.
Despite being the home of almost all of Nigeria’s petroleum reserves, the country’s south is as desperately poor as the rest of the country, which is Africa’s most populous with 140 million people.
But criminality and militancy are closely linked, with many of the militant groups accused of stealing crude oil from wells and pipelines for sale in overseas market and helping politicians rig elections. (reports from AFP and AP)