A curfew has been imposed in the north-eastern Nigerian city of Bauchi, after violence on Sunday in which at least 39 people were killed.
A Red Cross official told the BBC the whole city was silent. He said no-one knew the exact number of dead, as the mortuary was being guarded by the army.
Officials said clashes erupted when 60 Islamist militants armed with guns and explosives attacked a police station.
They said security forces repelled the attack and arrested around 170 people.
Authorities said the militants belonged to Boko Haram, a group that wants Sharia law imposed across Nigeria.
Islamic law has been in effect in the state of Bauchi since 2001.
One report put the death toll from Sunday's attack as high as 50, but there were conflicting reports of the number of casualties.
"The security took control of the corpses and started to transport them to the mortuary," Red Cross official Adamu Abubakarr told the BBC's Network Africa from Bauchi.
"Right now the... mortuary is well guarded by security so no one can tell exactly the number of corpses apart from them," he added.
The BBC's Caroline Duffield in Nigeria says the military is controlling all roads leading into the area.
The governor of Bauchi state, Isa Yuguda, told AFP the curfew would be in place "for as long as required to restore lasting peace" in the city.
Bauchi was the scene of clashes between Muslim and Christian communities in February that left four people dead.
Nigeria's 140 million people are split almost equally between Muslims and Christians and the two groups generally live peacefully side by side.