YOLA, Nigeria -- Nigerian troops killed scores of Islamic extremists and rescued 20 women and children from captivity even as reports came in Saturday of Boko Haram fighters slitting villagers' throats and chopping them to death.

That bolsters reports the insurgents are running out of ammunition and resorting to hit-and-run assaults in the face of a Nigerian offensive against their last stronghold, a northeastern forest.

"Despite continuous encounters with large numbers of land mines which still litter the Sambisa Forest, troops have forged ahead with the ongoing offensive operations as scores of the terrorists died in the assault on their bases on Friday," said a statement from Defence Ministry spokesman Maj. Gen. Chris Olukolade on Saturday night.

Four Boko Haram camps were destroyed in the assault in which one government soldier was killed and 10 wounded by land mines, he said. Many insurgent weapons, including armoured cars, were destroyed.

Meanwhile, farmer Kwada Abawu said he saw at least 10 people slaughtered by Boko Haram fighters before he fled his northeastern village of Kwamda-Kobla on Friday.

No shots were fired, according to Abawu and local government chairman Maina Ularamu. He said some victims were axed to death, others had their heads cut off.

He said civilian self-defence fighters were pursuing the attackers.

U.N. Secretary-General Ban Ki-moon said he "is deeply troubled by the continuing indiscriminate and horrific attacks by Boko Haram against civilian populations in Cameroon, Chad, Niger and Nigeria."

A statement released Friday said he regretted the continuing "wanton destruction and killing of civilians" despite recent gains by the Nigerian military.

The tide has turned against Boko Haram which earlier had seized scores of towns and villages and declared an Islamic caliphate across a swath of northeast Nigeria in an Islamic uprising that killed at least 10,000 people last year.

The turning point came when Nigeria acquired new weapons and helicopter gunships for its demoralized troops, and soldiers from neighbouring Chad, Niger and Cameroon joined the battle this year as Boko Haram attacks spilled over Nigeria's borders.

Nigeria's military announced in March that it had driven Boko Haram from all strongholds except camps in the Sambisa Forest.

The forest offensive has freed some 700 women, girl and children held captive by the extremists.