At least 360 people kidnapped by Boko Haram jihadists from a mainly Muslim community in Nigeria's north-eastern Borno state in March have been freed from a remote mountain hideout.

The circumstances of how they were freed are disputed. The army says it had launched an unprecedented intelligence-led operation that had been weeks in the planning and taken the Islamist militants by surprise.

But a local group, the Borno South Youth Initiative, says it mediated the unconditional release, putting the number of those freed at 416.

Mass abductions by groups for ransom have become a common tactic in Nigeria. Boko Haram gained notoriety in 2014 for kidnapping more than 200 schoolgirls from Chibok.

That spawned a range of groups that use kidnapping to raise funds, focusing on soft targets such as schools, churches, mosques and remote villages.

It is illegal to pay ransoms in Nigeria, but analysts say payments by desperate families, intermediaries or, in some cases, state authorities have fuelled the abductions.

Military spokesperson Lt-Col Haruna M Sani described the assault on Boko Haram's Mandara mountain hideout, "under cover of darkness", as one of the military's "most significant hostage rescue operations" in the north-east.

"Faced with the speed, precision, and overwhelming combat power of the advancing troops, several insurgents abandoned their positions and fled into surrounding mountainous terrain, while others surrendered," he said in a statement.

The authorities say the hostages are receiving medical care.

"Sadly, two infants died due to exhaustion from prolonged captivity and harsh terrain," Daniel Bwala, a special adviser to President Bola Tinubu, posted on X.

He said the government, which has been coming under fierce criticism for the widespread insecurity across Nigeria, commended the troops.

The captives are from around Ngoshe, a mainly Muslim community near the border with Cameroon.

In early March, the area came under attack from Boko Haram fighters reportedly as people were breaking their Ramadan fast.

Samaila Kaigama, president of the Borno South Youth Alliance (Bosaya), told journalists that his group had been advocating for their release and had been in contact with the militants.

In a video posted on Facebook he hit out at "government boys" who he said were "claiming glory for our efforts".

On Sunday morning, the military released videos and photos of the freed captives as they sat under trees overnight.

Several news outlets also had a video of a local government official telling them that the authorities were doing their utmost to secure the area so that they could go home to their farms.

He also explained that it was thought some of those captured were believed to have escaped into Cameroon and efforts were being made for their safe return.

Boko Haram began its military campaign to impose Islamic rule in northern Nigeria in 2009. It no longer controls the huge swathes of territory it once did, but it, and other splinter groups, remains active and dangerous.

Earlier this year, a small contingent of US soldiers deployed to Nigeria to train the West African nation's armed forces and help them with intelligence in their battle against growing security threats.

These are complex, overlapping and include the Islamist insurgency, kidnapping gangs, clashes over land and separatist unrest.

Last month, Nigeria and the US said they had killed a senior Islamic State (IS) leader in a joint-operation.