Survivors say suspected Islamic militants opened fire in a mosque in northeastern Nigeria and gunned down at least 20 worshippers.

Civil servant Musa Ibrahim said the gunmen struck before dawn Saturday as residents of Buni Gari village were gathering for the first prayer of the day.

The village is about 100 kilometres south of the Yobe state capital of Damaturu in an area that has been attacked numerous times.

Mosques have been a frequent target of militants who threaten Muslim clerics who preach against their extremist doctrine.

More than 1,200 civilians have been killed this year amid more frequent and deadlier attacks by the Boko Haram terrorist network that wants to create an Islamic state in Nigeria, a country of 170 million divided equally between Christians and Muslims.