At least 18 people and possibly many more have been killed in a clash between bandits and villagers in northwest Nigeria, police said on Friday, and President Muhammadu Buhari ordered security forces to track down those responsible.

Communal clashes have plagued swathes of Nigeria's hinterland despite pledges by Buhari since he took power in 2015 to improve security, especially in the northeast, which also faces an insurgency by the militant Islamist group Boko Haram.
A police statement said the final death toll from Thursday's attack in the village of Birani could well exceed the 18 confirmed deaths. Three villagers who witnessed the attack said more than 40 people had been killed.
The attackers came on motorcycles and opened fire on the villagers, Birani residents Hussaini Abdu, Salmanu Zurmi and Sani Musa told Reuters. They said the gunmen had also set fire to a vehicle with people inside.
"They slit the throat of the driver and then opened fire on the vehicle killing everyone on board and then set it ablaze," said Abdu, the village head.
Buhari has directed security agencies "to immediately mobilise and deploy their members to the vulnerable areas of the state, and to ensure that the perpetrators are brought to face the full wrath of the law", a presidency spokesman said.
He also sent his defence minister to the area to investigate the incident.
Nigeria has already deployed army troops to more than 30 of the west African nation's 36 states to help tackle insecurity.
Last month, Amnesty International said Nigeria's air force had killed at least 35 people in air raids on villages that were used as a "law enforcement method".