Nigeria's military says nine construction workers have been killed in the country's northeast, where militants from the Islamist group Boko Haram are active.
Military officials say the victims were working on a mosque in the city of Maiduguri.
A military spokesman told the Associated Press that the victims' throats were slashed in the attack early Monday.
Officials did not say who attacked the men. Maiduguri, the capital of Borno state, has repeatedly suffered attacks from Boko Haram.
It has claimed responsibility for many attacks in Nigeria, including church bombings and the bombing of a United Nations building.
Last month, the group claimed responsibility for attacking three Christian churches in Kaduna state. The attacks sparked reprisal attacks by Christians and led to days of unrest that left close to 100 people dead.
Boko Haram does not recognize Nigeria's government or constitution, and says it is fighting to establish a strict Islamic state.
Nigeria has a history of sectarian violence, especially in the country's Middle Belt, where the mainly Muslim north meets the predominantly Christian south.
Some information for this report was provided by AP and AFP.