They were travelling from the town of Sabon Birni to the town of Isa near the border with Niger.

Police spokesperson Sanusi Abubakar told the BBC that several others are being treated in a hospital for severe burns.

Some reports suggest the number of those killed is around 30.

One of those involved in evacuating the casualties described the scene as "horrendous" and that most of the victims were burnt beyond recognition.

The attack happened late on Monday but details are just emerging due to poor communication services in the area.

Some reports say the attackers deliberately set the vehicle on fire burning the occupants alive while another account indicates the fire ignited on the bus as a result of the attackers’ gunfire.

The police say they are investigating the circumstances of the attack.

Travellers are frequently targeted as the region continues to grapple with a wave of violence by armed gangs carrying out kidnappings for ransom as well as killings.