Nigeria-based Islamist militant group Boko Haram has said it was behind last week's kidnapping of hundreds of schoolboys in the north-western Nigerian state of Katsina.

More than 300 pupils are unaccounted for, but others managed to escape.

The authorities had previously blamed "bandits" for the attack.

Boko Haram has been notorious over the last decade for school kidnappings, including in Chibok in 2014, but these have taken place in the north-east.

In an audio message about the abductions, its leader Abubakar Shekau said "what happened in Katsina was our responsibility" and that his group opposed Western education.

This year hundreds of people in Nigeria's north-west region have been killed in attacks by what authorities have called criminal gangs, but until now it has been unclear whether they had links with Boko Haram.

The militant group has waged a brutal insurgency since 2009, mostly focused in north-eastern Nigeria. Tens of thousands of people have died and millions have been forced from their homes.

Residents living near Government Science Secondary School in Kankara told the BBC they heard gunfire at about 23:00 (22:00 GMT) last week on Friday, and that the attack lasted for more than an hour.

Security personnel at the school managed to repel some of the attackers before police reinforcements arrived, officials said.

Police said that during an exchange of fire, some of the gunmen were forced to retreat. Students were able to scale the fence of the school and run to safety, they said.

About 800 students were at the school when the attack happened and more than 300 are still missing - but it is not clear if all of them are being held by the kidnappers.

A 17-year-old boy who managed to escape the abductors told the BBC Hausa service how he crawled for several miles through the forest to freedom.

President Muhammadu Buhari comes from Katsina state, and is currently there on a private visit.

He was being briefed hourly on efforts to rescue the children, his spokesman Garba Shehu said.

The children believe that 10 of their schoolmates were taken by the bandits, but this still needed to be verified, Mr Shehu told the BBC.

He tweeted on Tuesday saying that Katsina Governor Aminu Bello Masari had met and briefed President Buhari about the operation to free the kidnapped students.

Many parents said they had withdrawn their children from the school, Governor Massari also ordered the immediate closure of all boarding schools in the state.