Tony Okonedo, a Shell spokesman, could not immediately confirm the attack.

"We have heard about the incident but we are still trying to confirm it," he said.

Shell, Nigeria's largest oil operator accounting for around half of the country's 2.1 million barrels per day output, has seen a wave of attacks on its facilities in recent months.

MEND, which came to prominence early 2006 has claimed responsibility for a series of attacks on Nigeria's oil industry and related sectors in the past two years.

Demands

The group has said they are fighting to force the federal government to send more oil industry revenue to their areas, which remain desperately poor despite decades of oil production.

The group also says it wants the release of one of its leaders, Henry Okah.

Okah is on trial in a closed court on treason and terrorism charges, which can carry the death penalty.

He was extradited to Nigeria earlier this year after his arrest last year in Angola.