LAGOS - NIGERIA'S main militant group said its fighters had attacked an oil facility belonging to Royal Dutch Shell in the Niger Delta on Monday, in the face of an amnesty offer from President Umaru Yar'Adua.

'The Nigerian supply disruptions brought in some buying,' said Mr Christopher Bellew, broker at Bache Commodities in London, adding crude futures could push above US$70 later on Monday.

Shell said it had shut in some production as a precautionary measure while it investigated reports of attacks on two well clusters in its Estuary Field in the western Niger Delta, which feeds into its Forcados oil export terminal.

'Hurricane Piper Alpha has struck at the Shell Forcados platform in Delta state today ... at about 3.30am (0230 GMT, 10.30am Singapore time),' the Movement for the Emancipation of the Niger Delta (Mend) said in a statement e-mailed to media.

It said parts of the facility were on fire.

Forcados is one of Nigeria's benchmark crude oil grades but production has been interrupted by militant attacks.

On June 17 Shell extended a force majeure on its Forcados oil shipments for the rest of June and all of July. The measure, which frees it from contractual obligations, was first imposed in March after an attack on its trans-Escravos pipeline.

Mr Yar'Adua on Thursday offered a 60-day amnesty to gunmen in the Niger Delta who have been responsible for pipeline bombings, attacks on oil and gas installations and the kidnapping of industry workers over the past three years.

The unrest has prevented the world's eighth biggest oil exporter from pumping much above two thirds of its installed capacity of 3 million barrels per day, costing it billions of dollars in lost revenue and pushing global energy prices higher.

Mend questioned the sincerity of the government and dismissed the amnesty offer as a programme directed at 'repentant criminals' rather than genuine 'freedom fighters'. -- REUTERS