Refugees had already fled from Sawmill last week
The fighting, which happened near the small town of Klay about 35 km (22 miles) from Monrovia, prompted President Charles Taylor to declare a state of emergency on Friday as armed rebels appeared to be gaining ground on the capital.
Government forces now seem intent on trying to block people fleeing Klay from entering the capital.
A BBC correspondent in the region says he saw several thousand refugees being held without vital supplies at an army checkpoint about 15km (9 miles) out of town.
No rebel or government troop casualties were reported, but there were reports of at least a dozen civilian graves being dug in the now deserted Klay, already swollen with refugees from fighting further north in the country.
Aid concerns
Aid workers in the region said attempts to reach those in need were being hampered by dangerous fighting.
"We don't know the whereabouts of thousands of people because we either don't have access or because we can't go there due to the security situation," Ramin Rafirasme, regional spokesman of the UN World Food Programme, told Reuters news agency.
"After years of war it doesn't take much for people to start taking their meagre possessions and (go on the) move," he said.
"We are extremely concerned about those displaced people."
Last week, the rebels also briefly captured the village of Sawmill just 80km from Monrovia, causing thousands of refugees to flee.
President Taylor announced the state of emergency hours after rebels first attacked Klay, although he made no reference to the fighting.
Complex conflict
However, following the attack the rebels appear to have melted back into the forest, our correspondent said.
Forces loyal to President Taylor have been fighting rebel factions in the north of the country since 1999.
But the BBC West Africa correspondent says the conflict in Liberia is complex and fragmented, with no clear rebel front-line outside Monrovia.
He says the rebels - if they exist as a coherent force at all - are a mixture of dissidents opposed to President Taylor and elements who would best be described as bandits.