* Attacks on oil facilities on the rise in Nigeria's Delta
* Sophisticated seawater attack signals escalation ofviolence
* Delta residents complain of neglect, poverty
By Ulf Laessing
LAGOS, March 4 (Reuters) - A sophisticated attack on asub-sea pipeline in Nigeria's Delta might herald a return to thekind of widespread militant violence that crippled the oilindustry in Africa's top producer less than a decade ago.
Attacks on oil facilities have been on the rise in theswamps since President Muhammadu Buhari vowed to shake up afraud-ridden amnesty programme for rebels who stopped blowing uppipelines in 2009 in exchange for cash and generous contracts.
Adding a new dimension, unknown militants - probably usingdivers - hit a Shell underwater pipeline last month,interrupting oil flows and forcing the company to shut down its250,000 barrel-a-day Forcados export terminal for weeks.
Nigeria-based diplomats and security experts say the attackshowed a level of skill and inside intelligence rarely seensince the 2004-2009 insurgency, which at its height halvedNigeria's oil output of around 2 millions barrels a day.
"This was an attack that required knowledge of the area andsophisticated equipment," said a Western security source, askingnot to be named. "There were underwater attacks before but nonerecently. The oil firms are really worried there will be more."
Militants tend to attack small overland pipelines or flowstations sitting in hard-to-access mosquito-infested creeks.
The underwater attack has cut 15 percent of Nigerian crudeoutput, dealing another blow to Buhari, who is already having tocope with a collapse of oil revenues due to falling prices, aBoko Haram jihadist insurgency in the north and secessionistcalls in the southeast.
The strike came a month after authorities issued an arrestwarrant for former militant leader Government Ekpemupolo, betterknown as Tompolo.
Like other ex-rebel leaders Tompolo became a millionairethrough the amnesty by winning contracts to protect pipelines heused to blow up in his fight for a greater share of Nigeria'soil wealth. Others made a fortune with massive oil theft.
Buhari has vowed to end over-priced state contracts andcrude theft. But in the Delta many ex-fighters see the hunt forTompolo as part of a campaign by mainly Muslim northerners, likethe president, against the Christian south. The governmentdenies any such motive.
The swampland's oil provides 70 percent of state income but,like much of the rest of Nigeria, the region has never seen muchdevelopment. Its roads are pot-holed and villages polluted fromoil spills.
"Many angry young men still support the militants becausethe government is not addressing their grievances," said AlagoaMorris, an environmental activist in the Delta. "They work foranyone who supports them."
TROOPS
Authorities have responded by sending troops to protect oilfacilities, a move residents say might fuel tensions asvillagers will likely see them as invaders sent by Buhari.
"The militarisation of the Delta makes it worse," saidMorris. "People see that the government is only interested inthe oil production, not their grievances."
A security official said Tompolo's men were probably behindthe sub-sea attack. Activists say it could have been the work ofother ex-rebels frustrated about the region's poverty.
Tompolo has disappeared from public view since the arrestwarrant was issued, and his spokesman, Paul Bebenimibo, couldnot be reached for comment.
He had links to the Movement for the Emancipation of theNiger Delta (MEND), one of the most powerful militant groups,which attacked oil facilities and kidnapped expatriate workers.
A previously unknown group called the Niger Delta Avengershas claimed responsibility, warning Buhari of more troubleunless he fulfils a long list of demands such as startingdevelopment and cleaning up polluted villages.
Reuters was unable to contact the group or verify itsstatement. In total, ten oil and gas pipelines or otherfacilities have been attacked in the Delta since the start ofthe year, security experts say.
DELTA
Tension has been building in the Delta since Buhari defeatedpresident Goodluck Jonathan, a Christian southerner from theregion, in presidential polls a year ago.
The government has extended the amnesty but vowed to shiftthe focus to job training and away from cash payments, which inthe past were collected by "generals" for their "boys".
So far, the attacks have not been as severe as the previousinsurgency. But diplomats worry that Delta activists are teamingup with secessionists in the southeast, where Ibgo people whoproclaimed an independent state called Biafra sparked a 1967-70civil war in which more than a million people died.
In the Avengers statement, the group demanded the release ofa pro-Biafra leader jailed since October.
On Thursday, groups of former militant leaders denounced thepipeline attacks but also urged Buhari to expand the amnesty to"some of our brothers who are still in the creeks" - still ahideout for militants, pirates and kidnappers.
They also told Buhari the amnesty should be extended to 2019to give young men time to receive job training.
The government has said it wants to set up vocationalcentres to train up to 10,000 people annually. But little hashappened as the oil price slump has undermined spending plans. (Additional reporting by Libby George in London, Felix Onuah inAbuja, Anamesere Igboeroteonwu in Onitsha and Tife Owolabi inYenagoa; Editing by Ed Cropley and Peter Graff)