Thirty-five bodies in military uniform have been brought to a morgue in Nigeria's restive northeast after a coordinated assault by Boko Haram targeting the security forces, a hospital source told AFP Monday.
The attack late Thursday in the Yobe state capital of Damaturu was the first raid in a major urban centre in several weeks by the insurgent group waging a four-year Islamist uprising.
Police and residents said large numbers of Boko Haram fighters, some in vehicles and some on foot, stormed Damaturu after dark.
Armed with guns and explosives, they attacked and torched four police buildings, sparking a fierce, hours-long gun battle with the security forces.
"We have received lots of bodies in the last three days from the attacks. I counted 35 bodies in military uniform," said a senior official at the Damaturu Specialist Hospital, who requested anonymity.
An army officer based in the central city of Jos said 20 soldiers had been admitted at a hospital there, suffering from "gunshot wounds sustained in the battle against Boko Haram in Damaturu."
"They were brought here for security reasons and better medical facilities," said the officer, who also asked his name be withheld.
The military rarely discusses troop fatalities following Islamist attacks and local officials who disclose such details have faced pressure to keep quiet.
Contacted by AFP on Monday, Yobe state military spokesman Lazarus Eli did not deny reports that dozens of soldiers were killed during the clash.
"We do not have any data on the death toll," Lazarus said.
Defence spokesman Chris Olukolade disputed the figure of 35 but said the military sustained losses.
"On the part of the military, we did not suffer that volume of casualties at all," he said, while adding, "definitely there were casualties on both sides."
Boko Haram has repeatedly worn military uniforms as a disguise during attacks and it was not yet clear whether the corpses were those of insurgents or troops.
The day after the attack, witnesses and local officials did not say the insurgents who staged it were disguised in uniforms.
Nigeria's sweeping offensive against Boko Haram has entered its fifth month, and the military has described the group as being in disarray and no longer capable of attacking major population centres.
But the success of the operation remains unclear and the attack in Damaturu, apparently carried out by a significant number of insurgents in a heavily fortified city, has cast further doubt on the effectiveness of the military offensive.
There are however signs that Boko Haram has been pushed back into the northeast, its historic stronghold, after carrying out attacks across the wider north through much of 2011 and 2012.
President Goodluck Jonathan declared a state of emergency across the northeast in mid-May and vowed to permanently end the uprising. Jonathan must decide whether to extend the emergency measures when the six-month mandate expires next month.
The conflict has killed thousands since 2009.
Boko Haram has attacked Christians, Muslims, students, politicians and a range of other groups seen as opposed to the creation of a state governed by strict Islamic law.
Nigeria is Africa's most populous country and top oil producer, where the northern half is mostly Muslim and the more prosperous south is predominately Christian.