Two gunmen on a motorcycle opened fire in the mainly Christian village of Tashan Alade, 230 kilometres (over 140 miles) from the Borno state capital Maiduguri, on Saturday, said police commissioner Lawan Tanko.
"The attackers, who were obviously Boko Haram insurgents, arrived at the open-air venue of the party around 2:00 pm (1830 IST) and opened fire, killing seven people and injuring five others," he told AFP.
"The gunmen fled immediately and escaped before security personnel could be alerted due to the remoteness of the village."
The wedding was attended by both Christians and Muslims, they added.
More From This Section
People injured in the raid were taken to hospital in Maiduguri, where a number died from gunshot wounds, said one hospital worker, who requested anonymity.
"Twelve people were brought here on Saturday with very serious gunshot wounds from Tashan Alade," the source added.
"Five of the injured died yesterday (Sunday)."
The seven others were said to be in a serious but stable condition.
Nigeria's government in May imposed a state of emergency in Borno and two other northeastern states, Yobe and Adamawa.
The operation -- assisted by civilian vigilante groups -- has seen Boko Haram fighters forced out of Maiduguri into more remote, rural areas on the border with neighbouring Cameroon, Chad and Niger.
The military has said that Boko Haram was now crossing the notoriously porous borders in the region to mount attacks before retreating.
Kwajaffa is near the Sambisa Forest, where Boko Haram has been engaged in fierce fighting with the military.
There were also reports of further deaths in the village of Warabe, also near Sambisa Forest.