* Militants say attack Shell oil well head

* Third attack since president's amnesty offer

* Militant group threatens more attacks on oil industry

 

(Adds military confirmation, vessel attacked)

 

By Nick Tattersall

 

LAGOS, July 5 (Reuters) - Nigerian militants said on Sunday they had launched their third attack on Royal Dutch Shell 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 had no further details.

 

There was no immediate confirmation from Shell.

 

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.

 

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 said it 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.

 

Fighters from MEND also attacked two well clusters in Shell's Estuary field on Monday, forcing the Anglo-Dutch giant to shut in some production as a precaution.

 

FURTHER ATTACKS?

 

MEND first burst onto the scene at the end of 2005, knocking out more than a quarter of Nigeria's oil output -- then some 2.4 million barrels per day (bpd) -- in a matter of weeks.

 

Oil production in the OPEC member country, the world's eighth biggest crude oil exporter, has never fully recovered and the militants have continued to nibble at infrastructure, preventing international oil firms from carrying out repairs.

 

MEND's latest campaign follows the military's launch in May of its biggest offensive for at least a decade, using helicopter gunships and battalions of ground troops to hunt down suspected militants in the western Niger Delta.

 

One of the group's key demands is that the amnesty offer be extended to its suspected leader Henry Okah, who is on trial for treason and gun-running and could face the death penalty. MEND says Okah needs urgent medical attention for a kidney ailment.

 

Yar'Adua has asked Interior Minister Godwin Abbe to extend the clemency offer to Okah, but he has so far failed publicly to do so and Okah's trial continued last week.

 

"The government's insincerity is the main cause (of the amnesty offer not working)," MEND said on Saturday in a statement which accused the security forces of attacking a community near oil facilities and burning it down after residents had fled.

 

"(This) will be revenged and it is the oil companies that will bear the brunt," the group said.

 

Some security analysts expect the military to launch another major offensive against militants who do not accept the amnesty once the 60-day offer period ends in October. (For full Reuters Africa coverage and to have your say on the top issues, visit: http://af.reuters.com/ ) (Editing by Tim Pearce)