A suspected Boko Haram attack in a northeast Nigerian village left at least 151 people dead last week, with many drowning as they attempted to flee across a river.

About 140 people died in the river near the village of Yadin Kukuwa and 11 were killed after they were shot by the Islamist militants on Aug. 13, Tasiu Sammani, a resident said by phone on Tuesday. News of the attack was delayed as phone masts in the area had been destroyed in previous raids.

"They came in large numbers on motorcycles and cars, raided our town and shot people," said Tanimu Magaji, another resident who had taken refuge in the city of Damaturu. "Some died from the gunshots and many others drowned in the river as they fled the scene. I lost my brother to the attack."

While nobody claimed responsibility for the attack, Boko Haram has killed thousands of people in its six-year campaign to impose its version of Shariah, or Islamic law, in Nigeria. President Muhammadu Buhari has pledged to crush the insurgency.