At least 200 people in Nigeria's northwestern Zamfara state have been killed in a wave of vicious attacks by armed militants, residents say.

The attacks are believed to be in response to military air strikes that killed more than 100 fighters on Monday and forced others from forest hideouts, reports BBC.

Gunmen burnt homes and mutilated the bodies of their victims in the assault.

A resident of one of the villages told the Reuters news agency the militants were shooting "anyone on sight".

The attacks are the latest in a wave of violent attacks in northwest Nigeria, where the central government has long been at war with a number of local criminal groups it has described as bandits.

On Friday it was initially reported that more than 100 people had been killed by suspected "bandit" militants in the region, after some 300 gunmen on motorbikes arrived in as many as nine communities between Tuesday and Thursday night.

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Idi Musa, a resident of another village, told AFP that the attackers also stole "around 2,000 cattle".

Meanwhile, local media has reported that armed groups appear to be abandoning hideouts in forested areas in response to sustained government attacks, instead moving towards the western part of Zamfara state.

In a statement issued on Saturday, Nigeria's President, Muhammadu Buhari, pledged that the government would not relent in its battle with the militants.

"Let me reassure these besieged communities and other Nigerians that this government will not abandon them to their fate because we are more than ever determined to get rid of these outlaws," Mr Buhari said.

"The latest attacks on innocent people by the bandits is an act of desperation by mass murderers, now under relentless pressure from our military forces."

On Wednesday, the Nigerian government officially labelled bandits as terrorists, allowing security forces to impose tougher sanctions on the groups and their supporters.

Nigeria's armed forces said this week they had killed 537 "armed bandits and other criminal elements" in the region and arrested 374 others since May last year.

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Thousands of Nigerian troops have been deployed to fight the armed groups, a sophisticated networks of criminals who operate across large swathes of territory, often stealing animals, kidnapping for ransom and killing those who confront them.