Motorbike-riding gunmen have shot dead at least 15 civilians and injured many others in the north-western Nigerian state of Sokoto.

The killings happened in the early hours of Monday.

The state governor, Aminu Tambuwal, who confirmed the attacks in a statement, said 13 of the victims were killed in the town of Illela on the border with Niger.

Two others were killed in a separate attack in Goronyo - a town where armed men carried out a massive attack last month, killing more than 40 people at a market.

Reports indicated many residents have fled their homes following the latest attacks.

The region is grappling with a wave of killings and kidnappings for ransom by armed gangs, which continue despite the deployment of thousands of security forces.

Over the weekend, militants affiliated to the so-called Islamic State group killed several members of the Nigerian security forces including an army general in an ambush in Borno state.