A splinter group of Boko Haram stormed Kukawa, taking hostage hundreds of residents whose fate remains unknown even after the army says it's retaken control.
They have seized those who had returned to the town in a government operation on August 2 after spending nearly two years in displacement camps.
An official said explosives that were fired from outside the city "landed on separate sites."
Insurgents fired rocket-propelled grenades at a lorry carrying troops as it travelled near Gorgi village in Borno state, two military officers said without giving their names.
Militants targeted the village of Auno on a key highway linking to regional capital Maiduguri, officials say, adding many women and children were abducted in the raid.
Mercy Corps says it's suspending operations in Borno and Yobe states after Nigerian military shut four of its field offices. Separately, Daesh-linked militants executed one of six captive aid workers of Action Against Hunger.
The global rights watchdog urged Nigeria to release the children – some as young as five years – detained in degrading and inhuman conditions in military cells, in a report rejected by the Nigerian army.
More than 40 people were also wounded when three unidentified bombers struck in the northeast state of Borno where villagers were watching a football match on TV, officials and villagers say.
Many Nigerian women who were once married to Boko Haram fighters are navigating their trauma, though by not denying their experiences. They also want to raise their children in anonymity, hoping their true identity is never revealed.
The attack was carried out in Kareto village, 335 kilometres north of the Borno state capital Maiduguri, military officials say.
Army spokesman Ezindu Idima said in a statement government troops "had a fierce encounter" before thwarting the militants who came in large numbers to loot food items and other valuables.
Some hours before the opening of polls on Saturday, multiple explosions rocked the northeastern city of Maiduguri, perhaps in a daring attempt to breed fear and discourage voting.
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