Three Nigerians have died in clashes in Lagos as soldiers fought running battles with police.
The dead were civilians caught in the crossfire of a battle that began when a soldier and policeman argued over who had the right to a free ride on a bus.
The police officer hit out at the soldier, who raised the alarm at a nearby barracks, sparking violence.
Soldiers and police then exchanged live fire across the main highway in Lagos, the country's largest city.
Some 60 vehicles, including 20 police cars, were set ablaze during the clashes.
Troops were reported to have stormed a police station, setting it on fire and freeing scores of prisoners.
"They were shooting at the police and the police were shooting back," local resident Kanayo Azubogo told the Associated Press.
"The soldiers went to the Western Avenue police station and set it on fire."
One police officer described the scene as "like a war".
The BBC's Sola Odunfa in Lagos says that there were several different versions of how the violence began, but the most common account was that the soldier and policeman came to blows after disagreeing over which of them had the right to a free ride in a bus.
The established practice is that one member of the security forces does not have to pay a fare on any bus.
The violence that followed was the worst of its kind in recent years, he said.
Law enforcement throughout Lagos broke down for about five hours, as uniformed policemen deserted streets across the city for fear of being attacked.
Senior officers eventually visited the scene of the clashes and re-asserted control.
The governor of Lagos, Bola Tinubu, and Police Commissioner Ade Ajakaye appealed for calm from all sides.