The Liberian capital, Monrovia, will be cleared of weapons by Thursday, says the head of the United Nations peacekeeping team.
All sides must keep their weapons out of Monrovia
Kenya's General Daniel Opande said he would set up a "systematic cordon" to ensure that all sides respected Monrovia's arms-free status.
The announcement followed a meeting attended by both rebel groups and the government.
Peacekeepers have brought relative stability to Monrovia since they arrived in August but skirmishing continues elsewhere in the country.
The government accuses rebels of attacking them in the north-eastern Nimba county.
The BBC's Jonathan Paye-Layeleh says that security checks on vehicles have been stepped up since the West African peacekeepers became the vanguard of the world's largest UN peace team - 15,000 strong.
Peacekeepers have made an impact on the capital
The peacekeepers are not due to deploy outside Monrovia until reinforcements arrive.
Last week, the UN special envoy to Liberia, Jacques Klein, warned that fighting could escalate until the extra troops were in place.
On the day West African peacekeepers became part of the UN force, a gunbattle broke out when the Lurd leader, Sekou Conneh, arrived in Monrovia for a meeting with interim president Moses Blah.
A battalion of troops from Bangladesh is expected later this month, the UN says.
Under the ceasefire agreement, a power-sharing government is due to take over next week, led by neutral businessman Gyude Bryant.