Suspected Islamist insurgents who hid weapons inside a coffin have shot dead 13 people in an attack targeting informants in the northeastern city of Maiduguri, two witnesses said on Sunday.
Friday's attack came as Nigeria's military makes its most concerted effort yet to end a four-year insurgency by Boko Haram, a sect that has killed thousands in a campaign to create a state governed by Islamic law in Nigeria's northeast.
Fearing the northeast was turning into a de facto Islamist enclave similar to northern Mali before French military action in January, Nigerian President Goodluck Jonathan declared a state of emergency last month in three states.
The military claim to have driven Boko Haram fighters out of Maiduguri and from their camps near borders with Chad and Niger.
But around ten men pretending to be driving to a burial came to an area of Maiduguri late on Friday, pulled the guns from the coffin and opened fire on some houses where vigilantes who aid the military live, witnesses said.
"The Boko Haram killed 13 residents during their sporadic gunshots," said an eyewitness, Saleh Ibrahim. He said soldiers later shot dead six insurgents whose bodies were left by the road.
A spokesman for the military joint task force (JTF), Sagir Musa, declined to comment on the attack but said vigilante groups in the area of Maiduguri targeted by the gunmen had helped identify Boko Haram suspects.
"People have been assisting the JTF with information to arrest the Boko Haram, so they were not happy and they came to deal with people there," said another witness, Ali Musa.
Boko Haram and other Islamist groups like the al Qaeda-linked Ansaru have become the biggest threat to stability in Africa's second-largest economy and top oil producer.