An armed gang killed at least 18 people in the northwest Nigerian state of Katsina, police and residents said on Wednesday, as unrest spreads across the region and into the president's home state.Hundreds of people have died in Nigeria's northwest since the beginning of the year, in attacks the government attributes to bandits, a loose term for gangs of outlaws carrying out robberies and kidnappings.Despite military and police operations to quell the conflict, the death toll continues to rise, along with incidents of kidnapping and robbery.Security experts say Nigeria can ill-afford more instability, with the country already struggling to contain Islamist insurgencies in the northeast, brutal pastoral conflict in the central states and militant groups in the Niger Delta to the southeast.In the latest incident, bandits attacked farmers at the village of Yar Gamji, near Nigeria's border with Niger, on Tuesday morning killing 18 of them, police said.The attackers escaped into a nearby forest, police said in a statement.Residents said that while 18 bodies had been found, many more people were feared dead."Right now we are at the Emir's palace for the mass burial of our relatives, but more than 18 people were killed in this attack," said Hassan Ibrahim, whose brother was killed."There is no peace in Katsina," he said. "Almost every day they carry out attacks on villagers, killing innocent people."