UN troops loaded three bodies on to a truck in the debris-strewn main street of the Paynesville suburb where the violence first erupted overnight, while residents peered out from behind doors after a daylight curfew was imposed.
A petrol station was ablaze and smoke rose from a torched building. White UN pickup trucks and armoured vehicles cruised the normally bustling streets, empty but for sticks, rocks and burned-out vehicles, while a helicopter hovered overhead.
Witnesses said a dispute between Muslim and Christian residents near Paynesville late on Thursday had mushroomed into a full-scale riot by Friday morning and then spread to the hilly centre of the coastal port city.
An aid worker at a Paynesville hospital said they had taken in 17 injured people, some with gunshot and machete wounds.
Liberia became a byword for anarchy and brutality in an already turbulent region during nearly 14 years of civil war but sectarian violence is unusual and the government blamed a "small group of misguided individuals" for stirring up trouble.
"Today the forces of darkness attempted to disrupt the peace and security of our country," said interim leader Gyude Bryant visiting Paynesville, where places of worship and gas stations owned by Muslims were torched.
Liberia suffered from 14 years of
bloody civil war
"The perpetrators of evil, in pursuit of their objective of keeping this country in a state of perpetual anarchy and chaos, decided to use the peace-loving Christians and Muslims of Liberia to attack each other," he said.
Sporadic gunfire could still be heard in Paynesville late on Friday afternoon.
Liberia is struggling to emerge from its protracted war. The impoverished West African country is home to 15,000 United Nations troops, the biggest peacekeeping force in the world.
More than 80,000 fighters have been disarmed but with a crippled economy, massive unemployment and few opportunities, youths, many of them ex-combatants, vent their anger and frustration by rioting.
The government said Taylor's
supporters provoked violence
Liberia's information minister, William Allen, said the curfew would remain in force until further notice and Bryant said UN troops were authorised to use "lethal force" to curb violence or looting and enforce the curfew.
Allen accused members of exiled former President Charles Taylor's party (NPP) of plotting to whip up violence to disrupt the UN disarmament programme, which is due to end shortly.
Earlier on Friday, young men clutching sticks and machetes roamed streets near Paynesville while UN peacekeepers blocked a main road and tried to chase rioters back.
In the centre of Monrovia angry former fighters ran carrying petrol canisters on their heads looking for things to burn. Thick smoke rose from a building in the town centre.
Residents brought the body of a young man to the office of the UN special envoy to Liberia, Jacques Klein, saying he was shot by peacekeepers near the German embassy. There was no independent confirmation of how the student had died.
UN armoured vehicles and blue-helmeted soldiers lined a street in the Mamba Point district that is home to most of the UN agencies and the US embassy.
During the civil war battle lines were usually drawn along loose ethnic or regional lines, rather than religious ones.
About 20% of Liberia's population is Muslim, 40% Christian and 40% follows animist beliefs.