New Delhi, Aug. 20 -- Gunmen attacked a mosque in northwestern Nigeria on Tuesday morning, killing at least 13 people during morning prayers, local authorities said.

No one immediately claimed responsibility for the attack in the town of Unguwan Mantau, in the state of Katsina, but such attacks are common in Nigeria's northwestern and north-central regions where local herders and farmers often clash over limited access to land and water.

The attacks have killed and injured scores - last month, an attack in north-central Nigeria killed 150 people. The prolonged conflict has become deadlier in recent years, with authorities and analysts warning that more herdsmen are taking up arms.

The state's commissioner, Nasir Mu'azu, said the army a...