By Julia Payne

ABUJA (Reuters) - Video footage found in captured Boko Haram camps by Nigeria's military and seen by Reuters seems to give some of the clearest indication that foreign fighters hold positions of power within the Nigerian Islamist militant group.

The military says it is analysing the footage to identify fighters and study the group's internal dynamics.

The Nigerian government has previously spoken of foreign influence within the ranks of the jihadists but lacked hard evidence to back up its assertion.

"They (foreigners) carry arms and fight alongside the other terrorists," a senior military source, who declined to be identified, said. "They are also experts and trainers."

Reuters was not able to establish how many other foreigners were at the filmed event or what percentage of the militants' fighting force they account for overall.

In 2012, Boko Haram was reported to be receiving training from al Qaeda in the Islamic Maghreb (AQIM), although there has been little to back up claims of foreigners at the core of the group beyond anecdotal evidence from civilians who escaped or soldiers who fought them.

Boko Haram, which loosely translates as "Western education is sinful" in the northern Hausa language, began an insurgency in 2009 to establish a state adhering to strict sharia law.

The footage shows Boko Haram administering sharia judgments in front of a big crowd in a field stained with blood with a man speaking in Sudanese Arabic.

"God ordered all believers to enforce his punishments," the man, whose face is completely covered by a white turban, says to camera. "God ordered us to cut off the hand of the thief and flog the adulterer and adulteress."

SHARIA LAW

Standing in the middle of a circle formed by the crowd and near a preacher shouting into a loudspeaker in Hausa, the man appeared to be overseeing at the gathering called to implement sharia law.

A man wearing a black turban stands next to him as he speaks in Arabic and occasionally nods in agreement while another waves the group's black flag behind them. Turbans in this style are not typical in Nigeria's northeast.

Story continues

In other parts of the film, men and women are flogged and several have hands amputated while the crowd cheers. A man is also stoned to death after being buried up to his head in a pit.

The military says it believes the events took place in southeastern Borno state in or near the town of Gwoza, Boko Haram's former headquarters. The distinctive Mandara mountain range can be seen in the background. There was no time stamp to indicate when the half hour of video was filmed but a shorter, edited version of the film was released after the group took over Gwoza last summer.

The discovery of the footage was reported in local Nigerian media and Reuters made a request to view the footage, which was granted by the military. The Nigerian military has not publicly released the footage while its analysts worked on identification and the workings of the group.

"It (footage) helps document their atrocities as evidence in the event of any trial," a senior military source said, adding:

"To understand their pattern or mode of operation ... and equipment in their possession with other information, is vital for intelligence." Reuters was unable to independently authenticate the footage and Boko Haram could not be reached for comment. Reuters viewed four separate videos.

BOKO HARAM LESS MEDIA SAVVY

Boko Haram started as a clerical movement in Nigeria's Borno state capital, Maiduguri, with a core membership from the Kanuri ethnic group spread around the Lake Chad basin.

Boko Haram is less media savvy than the Islamic State in Syria and Iraq, to which it pledged allegiance in March.

The Islamic State is known for its slick, technically proficient propaganda videos, which attracted fighters from around the world.

Far less is known about Boko Haram's internal structure or how it ran the towns it took, though survivors recount rapes, starvation and beatings.

Reuters also saw raw footage of a video titled "Harvest of Spies", released in edited form in March, which copied Islamic State videos and showed the beheading of two men accused of being undercover government agents.

The six-year Boko Haram insurgency has seen thousands killed and many abducted. Boko Haram kidnapped more than 200 schoolgirls near the northern village of Chibok in April 2014, causing international outcry.

Nigeria's army said it has freed over 700 women and children in the last month during an operation to wrest back the Sambisa Forest, a vast former colonial game reserve.

The group, notorious for violence against civilians, controlled an area roughly the size of Belgium at the start of the year but has since been beaten back by Nigerian troops, backed by Chad, Niger and Cameroon.

Nigeria has regained most of the territory since February and launched an offensive last month to root the militants out of their last stronghold in the Sambisa forest.

Boko Haram has been splintered but is not completely quashed. There are signs already that it is returning to its old guerilla-style tactics after attacking Maiduguri and hitting several other towns, including with suicide bombers.