Gunmen suspected to be armed robbers have killed 20 people in a village in the northwest Nigerian state of Zamfara, authorities said on Wednesday, a similar attack to one in June.Dozens of men armed with guns stormed Kaburu village early on Tuesday morning, demanding money before shooting and hacking people to death, local residents said."They were all shot to death while the village head was slaughtered with a sword,” local government spokesman Salihu Anga told Reuters by phone.At least 27 people were killed in June when suspected armed robbers attacked several villages in Zamfara.Islamist sect Boko Haram has killed hundreds across the north this year in its campaign for an Islamic state in a country split roughly equally between Christians and Muslims.Boko Haram mostly attack in northeastern Borno state and its capital Maiduguri, the sect’s base, but a recent military crackdown there has pushed its insurgency into other areas.On Sunday, a suicide bomber drove a jeep full of explosives into a church in Kaduna, about 70 miles (113 km) from the Zamfara border, killing eight people and triggering reprisals that killed at least two more.A breakdown of law and order has created opportunities for armed gangs driven more by money than ideology.Nigeria’s mainly Muslim north celebrated the Islamic Eid al-Adha holiday at the end of last week. Violent crimes often increase in Nigeria around holidays when people carry more cash.Zamfara, at the base of the Sahel in the far northwest of Africa’s most populous nation, shares a border with Niger.