Authorities in Nigeria's northeastern Borno state have imposed a 24-hour curfew on the main city of Maiduguri after an attack early Monday by suspected Boko Haram militants.
A government statement announcing the curfew pleaded for calm but did not give additional details about the attack.
Local reporters told VOA there were sporadic attacks overnight in the area of the city's airport. A soldier and others living in the area described it as a big attack.
There was no immediate information on any casualties.
The curfew is the first the state government has imposed since 2009.
Borno is one of the areas where President Goodluck Jonathan declared a state of emergency in May as part of efforts to defeat the Islamist Boko Haram.
Nigeria's military says it has killed scores of militants and destroyed several of the group's camps, but that attacks against civilians continue.
Boko Haram is blamed for thousands of deaths in attacks since 2009.
Boko Haram is believed to want to impose strict Islamic law across Nigeria's Muslim-majority north. The fight against the group is complicated by uncertainty about its structure and leadership, and questions about whether criminals are using the group's name as cover for their activities.
Rights groups have also accused the military of using indiscriminate and heavy-handed violence in its efforts to crush the group, and causing hundreds of civilian deaths.