Nigerian soldiers participate in an operation in Nigeria's northeastern state of Borno, March 16, 2016. (Xinhua/Wale Salau)

ABUJA, Dec. 20 (Xinhua) -- Twenty Boko Haram fighters have been killed by Nigerian forces in an ongoing operation to rout remnants of the terrorists, the Nigerian military said Wednesday.

Timothy Antigha, the army spokesman, said 17 other Boko Haram fighters were captured by the military strike force fighting to smoke out the terrorists inhabiting remote islands in Lake Chad basin within the Nigerian territory.

Antigha said following the military operation, which started about two weeks ago and was preceded by coordinated air and artillery bombardment, the Nigerian troops rescued over 100 elderly men, women and children.

According to the spokesman, six soldiers who were injured during the operation are receiving treatment at a military medical facility.

A preliminary investigation revealed that many of the rescued people were held against their will and forced to work on farms with penurious wages, Antigha noted.

Nigeria has made a considerable gain on the Boko Haram front, with its security forces having dislodged Boko Haram fighters from the Sambisa Forest, their last enclave in the country.