Suspected militants from Nigerian Islamist group Boko Haram have hijacked a bus in northern Cameroon, abducting at least 20 people, residents say.

Militants reportedly seized a bus carrying market-goers and drove it toward the border with Nigeria.

Some reports put the total number kidnapped in Cameroon as high as 30.

Boko Haram has escalated its attacks outside Nigeria in recent weeks, targeting neighbouring Cameroon and Niger.

The bus was seized near the border area of Koza and driven towards the Nigerian border 11 miles (18km) away, a resident told the Associated Press.

In an apparently related incident, several Boko Haram fighters were killed and 10 Cameroonian soldiers injured as the militants attacked Kerawa, a local journalist told the BBC.

A separate group of fighters reportedly attacked the nearby town of Kolofata, looting food and livestock.

The attacks in Cameroon follow a series of assaults on the border region of Diffa in Niger.

The militants targeted a prison in the region on Monday but were repelled by Nigerien troops.

The Boko Haram insurgency has led to more than a million people fleeing their homes, and the conflict is now poised to draw in neighbouring countries threatened by the group.

On Saturday Nigeria and the governments of Cameroon, Chad, Niger and Benin agreed to establish a force of 8,700 troops, police and civilians to fight the group.

Niger's parliament was due to vote on Monday on whether to contribute 700 of its troops to the force.

Presidential and parliamentary elections due to take place on 14 February have also been postponed to 28 March, and elections for state governors and assemblies slated for 28 February have been moved to 11 April.