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At least 20 of up to 80 people taken hostage by Boko Haram militants in Cameroon at the weekend are reported to be free.

Cameroon's defence ministry said the hostages were freed "as defence forces pursued the attackers who were heading back to Nigeria".

Many of those kidnapped in the cross-border raid were said to be children.

It was one of the biggest abductions by Boko Haram outside Nigeria and raised fears that it is expanding its attacks.

The militant Islamist group has seized control of towns and villages in north-east Nigeria and has begun threatening neighbouring countries.

Chad, which also borders Nigeria, has recently sent soldiers to help Cameroon tackle the militants.

Homes burned

The abductions took place in the villages of Maki and Mada near the city of Mokolo in Cameroon's Far North region.

Cameroonian police and officials said the militants had arrived in the early hours of Sunday morning when it was still dark. Many of those seized were said to be women and children.

Before leaving, the attackers burned dozens of homes to the ground.

It was not immediately clear how those hostages who are now free became detached from the main group.

Cameroon has not given details about its military operation and there has been no word from those freed or from the militants.

On Friday, Ghana's President John Mahama said African leaders would discuss plans this week to "deal permanently" with Boko Haram, and suggested a multinational force may be considered.

Niger and Cameroon have criticised Nigeria for failing to do more to stop Boko Haram's attacks.

Correspondents say Nigerian politicians appear more focused on campaigning for elections next month than on security issues, and senior figures rarely comment on the insurgency in the north-east.