UPDATE 4-Nigeria militants attack Shell, amnesty hopes fade

* Militants say attack Shell oil well head

* Third attack since president's amnesty offer

* Militant group threatens more attacks on oil industry

(Adds Shell says investigating)

By Nick Tattersall

LAGOS, July 5 (Reuters) - Nigerian militants said on Sunday they had launched their third attack on Royal Dutch Shell (RDSa.L) since President Umaru Yar'Adua made an amnesty offer, and threatened to intensify their campaign of sabotage.

The Movement for the Emancipation of the Niger Delta (MEND) said in an emailed statement it had attacked a Shell oil well head in the Cawthorne Channel at about 0200 GMT, again dashing hopes that the amnesty offer would buy a period of calm.

"The facility connects to the Bonny loading terminal in Rivers state," it said, referring to a key oil export terminal in the eastern part of the Niger Delta.

Colonel Rabe Abubakar, spokesman for the military taskforce which patrols the Niger Delta, said "miscreants" had attacked and damaged a facility in the Cawthorne Channel, causing damage to the environment. But he had no further details.

Shell said it had received reports of an attack in the area and was investigating.

A private security contractor said a vessel carrying chemicals was thought to have been attacked 20 miles offshore further west and six crew members kidnapped at about the same time. Abubakar could not immediately confirm that report.

Shell said on Tuesday the latest raids -- which had largely focused on the western Niger Delta -- had slashed output from its onshore facilities to 140,000 barrels per day (bpd), around half its production level earlier this year. [ID:nLU240107]

The disruption to supplies last week helped push global oil prices to an eight-month high above $72 a barrel.

Yar'Adua said 10 days ago he would offer a 60-day amnesty to gunmen to try to end unrest which has prevented Nigeria from pumping much above two-thirds of its installed capacity since early 2006, costing it billions of dollars in lost revenue.

Some militant leaders have indicated they would be willing to accept the offer, provided they can negotiate the terms. But MEND -- a loose network of various armed factions -- has doubted the government's sincerity.

The group blew up a Shell well head in Delta state hours after the amnesty proposal, accusing the military of going on a "punitive mission" to hunt down suspected militants despite the offer, a charge the security forces denied. [ID:LQ460625]