* Four grades of Nigeria oil under force majeure
* Violence shows little sign of abating
* President Muhammadu Buhari cancels Delta region visit (Adds Shell confirms leak)
By Libby George and Ulf Laessing
LONDON/ABUJA, June 3 (Reuters) - The Niger Delta Avengersmilitant group has claimed responsibility for three new attackson Nigeria's oil infrastructure, promising to cut production tozero.
The attacks are the latest in a Delta region conflict that amajor local youth group said is "rapidly deteriorating andgetting out of control", putting intense pressure on Nigeria'sstretched finances.
Early on Friday, the group said via its Twitter account ithad blown up a pipeline in Nigeria's Bayelsa state owned byItaly's ENI, hours after attacks on another ENIpipeline as well as one belonging to Shell Petroleum DevelopmentCompany of Nigeria Ltd (SPDC).
"At about 3:30am our (@NDAvengers) strike team blew up theBrass to Tebidaba Crude oil line in Bayelsa," the group said ona Twitter feed it uses to claim attacks.
Shell confirmed its 250,000 barrels a day Forcadospipeline had been hit again and was leaking. "We have ...mobilised appropriate oil spill response measures," SPDC said ina statement.
The pipe had been shut in February after a seawater attackbut a new strike might complicate three-month long repairs, forwhich the firm has brought in experts from abroad. Force majeurhas been in place for Forcados crude since then.
The Niger Delta Avengers say oil firms are responsible forpollution and say the poor swampland region fails to reap anybenefit from its reserves.
It said its attacks had brought Nigeria's oil production tojust 800,000 barrels per day (bpd), from 2 million bpd, withoutkilling anyone, though they hit infrastructure feeding crudegrades already under force majeure.
The ENI pipeline is used to transport Brass River crude.
The group also hit ENI's Ogboinbiri-Tebidaba and CloughCreek-Tebidaba pipelines in Bayelsa and warned ENI not to startrepairs or "we will make you regrets it".
ENI did not respond to a request for comment.
LOUD SOUND
Ayiri Appah, a resident of Ogboinbiri, where the ENIpipelines are located, said he "heard a loud sound" from thearea between 2 and 4 am local time.
Three grades of Nigeria's oil - Forcados, Brass River andBonny Light - are under force majeure, while Exxon Mobil lifted force majeure on Qua Iboe, the country's largest exportstream, on Friday.
Nigeria's oil minister said on Thursday that output was 1.6million bpd. Even if the most recent attacks, which alsoincluded facilities belonging to Chevron under itsEscravos grade, took out all exports of the oil linked to them,June production would remain near 1.2 million bpd.
Experts said the violence showed little sign of abating, andwould keep pressure on the Nigeria's oil production andfinances. President Muhammadu Buhari, a Muslim from the north,on Thursday cancelled what would have been his first visit tothe Delta region since taking office.
The Avengers have accused Buhari of ignoring local problemsby having never visited the Christian region in the south.
The Ijaw Youth Council, which represents one of the largestethnic groups, called on Buhari to "urgently and personally takecharge ... to return peace and normalcy to the region." (Additional reporting by Seng Li Peng, Florence Tan inSingapore, Ulf Laessing in Abuja, Anamesere Igboeroteonwu inOnitsah, Tife Owolabi in Yenogoa and Julia Payne in London;Editing by William Hardy and David Holmes)