Gunmen killed 26 people in Nigeria's northwestern Zamfara state, police said on Tuesday, in the latest violence to hit the troubled region.The attacks happened late on Monday in six neighbouring villages - Wonaka, Ajja, Mada, Ruwan Baure, Doka, Takoka, and Tudun Maijatau - in the state's Mada area.In a separate attack, armed bandits killed 11 people and torched homes in Batauna village, in Bukkuyum district.Details about the attack on Batauna were sketchy due to distance, inaccessible terrain, and a lack of telecommunications, said Zamfara state police spokesperson Mohammed Shehu. "The Zamfara state police command wishes to confirm the killing of 15 persons, including a female, following attacks on the six villages" in Mada, he stated."In another development... armed bandits stormed Batauna village and killed 11 persons and set several houses ablaze."Seven people were kidnapped during the attacks on the six villages but were later released, Shehu said.The spokesperson added that the Mada attacks were "presumably" reprisals for the killing last week of seven nomadic herders in the area by vigilantes who burnt the men together with their cattle.However residents of the six villages disputed the police's claim, insisting the attack was carried out by cattle rustling and kidnapping gangs which operate in the area."The attackers were no doubt bandits who have been stealing our herds and kidnapping our people for ransom," a local chief in the area told AFP on condition of anonymity.Farming and herding communities in Zamfara have long suffered attacks from criminal gangs who raid villages, steal cattle, kidnap residents for ransom and burn homes.Last July, Amnesty International said Zamfara state was "at the mercy" of armed bandits who had killed at least 371 people in the first six months of 2018. In April 2018, troops were deployed to fight the gangs, and police in December claimed to have killed 104 bandits following a clash in which 16 policemen died.The security situation in Zamfara is one of a number of challenges facing President Muhammadu Buhari, who is seeking re-election at polls this month.He came to power in 2015 on a promise to improve security in Nigeria but while he has made some gains against Boko Haram Islamists, several other conflicts have intensified.They include a resurgence of fighting in the long-running battle for resources between nomadic herders and farmers in central states.Northwestern Nigeria is Buhari's strongest regional support base and the criminality in the remote region has increased criticism even from within his own party.Last month, Information Minister Lai Mohammed claimed that bandits were mobilised to carry out attacks and "provoke massive chaos before, during and after the elections".Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.