On Boko Haram front line, Nigerian vigilantes amass victories and power

* Vigilantes take on Boko Haram with shotguns, swords

* Nearly 700 killed in action, leaders say

* Informal security forces demand pay, jobs

* Rights groups accuse vigilantes of abuse, extortion

* Observers in Nigeria fear militias being used in politics

By Ed Cropley

MAIDUGURI, Nigeria, June 15 (Reuters) - His broken arm is in a bamboo splint, his torso pock-marked with shrapnel and his jaw wired together by a Nigerian army surgeon.

But 38-year-old vigilante Dala Aisami Angwalla is undaunted by two nearly fatal brushes in the last year with Boko Haram, one involving a landmine, the other an ambush, and is determined to rid northeast Nigeria of the jihadists.

It is a sentiment shared by thousands of other volunteer vigilantes who have been instrumental in checking Boko Haram's progress but whose presence now casts a shadow over longer-term efforts to bring stability to the troubled Lake Chad region.

"Why do I do it? Because it's my country," the father-of-five told Reuters in Maiduguri, the capital of Borno state and epicentre of Boko Haram's bloody, eight-year campaign to build an Islamic caliphate in the southern reaches of the Sahel.

"My children are OK. When I go out, they say 'Go well, father. May God keep you safe,'" he said, fingering a charm around his neck that he believes keeps him from harm's way.

Angwalla belongs to the 30,000-strong "Civilian Joint Task Force" (CJTF) now fighting on the front line of Nigeria's struggle against Boko Haram after helping the military push the Islamists from towns across Borno in the last three years.

Despite a string of victories, the CJTF has drawn criticism.

Rights groups accuse its members of abuses ranging from extortion to rape and say their entry into the fray three years ago may be the reason for a sharp rise in Boko Haram violence against civilians.

CJTF leaders, who say 670 of its "boys" have been killed in action, say bar a "few bad people" its members are registered, impartial and professional.

FEAR OF ARMED GROUPS

The CJTF, most of whom are unemployed men, has asked the government to provide payment for its operations, a demand seen by political observers as ominous given the blurred lines in Nigeria between local politics and orchestrated violence.

With national elections in 2019 and the long-term illness of President Muhammadu Buhari pointing to a power vacuum, fears about organised armed groups are on the rise.

"In Nigeria in particular, vigilantism did much to turn an anti-state insurgency into a bloodier civil war, pitting Boko Haram against communities and leading to drastic increases in violence," the International Crisis Group, a think-tank, said.