Nigeria's main militant group said Sunday its fighters had attacked two Royal Dutch Shell oil pipelines in Rivers state, taking its latest offensive to the eastern Niger Delta for the first time.

The Movement for the Emancipation of the Niger Delta (MEND) said it had attacked Shell's pipelines at Adamakiri and at Kula, both in Rivers, early Sunday, as part of a series of strikes it has dubbed "Hurricane Piper Alpha."

"Piper Alpha unleashed its fury in Rivers state today... leaving in its wake two battered oil installations," the group said in a statement.

There was no immediate confirmation from Shell or from the Nigerian military.

The attacks are the first to strike Rivers state, the easternmost of the three main states in the Niger Delta, since the militants launched their latest campaign of sabotage following a military offensive in the western delta last month.

Persistent acts of sabotage by MEND over the past three years have cut oil output in the OPEC member, the world's eighth biggest crude oil exporter, to less than two thirds of its installed capacity of 3 million barrels per day (bpd).

The group first burst onto the scene in late 2005, knocking out more than a quarter of Nigeria's oil output -- then around 2.4 million bpd -- in a matter of weeks.

But the latest campaign has nibbled further at production.