* Delta swamps home to much of Nigeria's oil wealth
* New militant group threatens to launch new insurgency
* Pipeline attacks have reduced oil output by 300,000 bpd
* Little is known about the "Niger Delta Avengers"
By Tife Owolabi and Ulf Laessing
YENAGOA/ABUJA, Nigeria, May 13 (Reuters) - They callthemselves the Niger Delta Avengers. Little is known about thenew radical group that has claimed a series of pipeline bombingsin Nigeria's oil-producing region this year and evaded gunboatsand soldiers trawling swamps and villages.
Their attacks have driven Nigerian oil output to near a22-year low and, if the violence escalates into anotherinsurgency in the restive area, it could cripple production in acountry facing a growing economic crisis.
President Muhammadu Buhari has said he will crush themilitants, but a wide-scale conflict could stretch securityforces already battling a northern rebellion by hardline SunniMuslim group Boko Haram.
Militancy has been rife over the past decade in the Delta, asouthern region which is one of the country's poorest areasdespite generating 70 percent of state income.
Violence has increased sharply this year - most of itclaimed by the "Avengers" - after Buhari scaled back an amnestydeal with rebel groups, which had ended a 2004-2009 insurgency.
Under the deal, more state cash was channelled to the regionfor job training and militant groups were handed contracts toprotect the pipelines they once bombed. But Buhari cut thebudget allocated to the plan by about 70 percent and cancelledthe contracts, citing corruption and mismanagement of funds.
The "Avengers" have carried out a string of attacks sinceFebruary that reduced Nigerian oil output by at least 300,000barrels a day of output, and shut down two refineries and amajor export terminal.
On Thursday the group emailed journalists a statement sayingthey were fighting for an independent Delta and would step uptheir attacks unless oil firms left the region within two weeks.
"If at the end of the ultimatum you are still operating, wewill blow up all the locations," it said. "It will be bloody. Sojust shut down your operations and leave."
"To international oil companies, this is just the beginningand you have not seen anything yet. We will make you suffer," itsaid.
Authorities have no hard facts about the group - such as itssize, bases or leadership, Nigeria-based diplomats say.
Diplomats and security experts say it has shown a level ofsophistication not seen since the peak of the 2004-2009insurgency, which halved Nigeria's oil output. They say it mustbe getting help from sympathetic oil workers in identifying thepipelines to cause maximum damage.
"Its scary. Their demands are impossible to meet so therewill be probably more attacks," said a security expert, askingnot to be named.
GUNBOATS
In February the group claimed an attack on an underseapipeline, forcing Shell to shut a 250,000 barrels a dayForcados terminal. Last week, it took credit for blasting aChevron platform, shutting the Warri and Kadunarefineries. Power outages across Nigeria worsened as gassupplies were also affected.
There have been other smaller attacks and this week anotherexplosion, which bore the hallmarks of the group, closed Shell'sBonny Light export programme.
Reuters, like other media, has been unable to reach thegroup, which mainly communicates via Twitter, with the locationtracker switched off, and on its website.
Its members describe themselves there as "young, welltravelled" and mostly educated in eastern Europe.
Given the lack of intelligence about the militants, the armylaunched a wide-ranging hunt across the Delta this week, sendinggunboats into mosquito-infested creeks and searching villages inthe middle of the night.
But some residents say such a heavy-handed military approachstokes dissent in the Delta where many complain of povertydespite sitting on much of Nigeria's energy wealth. They saysome villagers help militants to hide in the hard-to-accessswamps.
"The military came at 12.30 am with two gunboats ... theywent from house to house. Many ran into the bush," saidGodspower Gbenekemam, chief of the Gbaramatu area.
"The military stayed on until about 5.30 am, during which nobody was able to move out," he said. "We are not part of thepeople blowing up pipelines. We do not know them so the militaryshould leave our community alone."
Alagoa Morris, an environmental activist based in the Delta,said unless soldiers acted with restraint, more people wouldjoin the militants, with a risk of "the Niger Delta returning toanother round of full-scale militancy".
Even oil majors, which have long pressed for better pipelineprotection, worry the tactics could backfire.
Executives met Vice President Yemi Osinbajo this week andone of them warned the government was being "too direct andblunt" and needed to find some balance, according to a sourcefamiliar with the discussions.
ULTIMATUM
The military has not said how many soldiers have beeninvolved in the sweep. The army searched several villages aroundGbaramatu because that part of the Delta is home to formermilitant leader Government Ekpemupolo, better known as Tompolo.
Some officials have linked Tompolo to the "Avengers",pointing to the fact that the attacks began after authoritiesissued an arrest warrant for Tompolo on graft charges inJanuary.
Tompolo has denied any ties, saying he himself is a victimas the group had asked him to apologise for criticising it.
For Buhari, the campaign against former militants is a partof his election promise to fix a country gripped by graft andmismanagement, but many locals in the Christian south see him, aMuslim northerner, as an oppressor.
Buhari's cutting of the amnesty plan's budget has alsocaused widespread resentment in the Delta, as it helps fund jobtraining for the unemployed.
Tapping into such anger, the "Avengers" point out that theformer military ruler has never visited the Delta, where manyroads are pot-holed and some villages are polluted from oilspills.
In a flurry of statements, the militants have published alist of demands, from cleaning up oil spills to keeping theamnesty plan, leading up to Thursday's ultimatum.
Diplomats say some of Tompolo's followers have probablyjoined the "Avengers" and that the group's ranks could beswelled by an army of unemployed willing to work for anyone.
But, adding to the confusion surrounding the group, someformer rebels have denied knowledge of the militants and saythey have brought unwanted military attention to the area.
"Niger Delta Avengers are not fighting for the sake of NigerDelta," said Eris Paul, a former leader of the now-defunctMovement for the Emancipation of the Niger Delta (MEND), whichwas one of the most powerful militant groups. "We don't knowthem." (Additional reporting by Anamesere Igboeroteonwu, Ron Boussoand Libbby George; Editing by Pravin Char)
