Liberian rebels are again engaged in fierce fighting with government forces near the capital.
Pro-government fighters are trying to hold the line near Monrovia
This is the third time in a month that fighters from the main rebel group, Liberians United for Reconciliation and Democracy (Lurd), have advanced to the edge of the city.
Hundreds of civilians have died in the fighting and many more have been forced to flee their homes.
The Liberian Government says it has lost control of the strategic Po River bridge.
The BBC's Paul Welsh in Monrovia says the bridge is the last big obstacle before another bridge, which leads into the suburbs of the capital city itself.
General Roland Anderson told our correspondent: "We least expected this, a ceasefire should be holding and if one group should come and want to foul it, the ceasefire, then it's terrible."
Aid worker Tom Quinn, writing in his diary for News Online, says that staff in the refugee camps north of the capital can hear small arms fire and mortars.
Meanwhile, according to a UN envoy, the United States will not take a decision on whether to send troops into Liberia until a local, West African force is in place.
The envoy, Jacques Klein, said the key thing was that troops from Ecowas - the Economic Community of West African States - should go into Liberia quickly, to end the clashes.
He said the Americans were willing to engage, but wanted to see the strength of the regional commitment first.
Jacques Klein, who recently took up the post as special representative of the UN Secretary General for Liberia, recently accompanied Kofi Annan on a trip to Washington and was party to discussions about the possible deployment of American troops to help restore law and order in Liberia.
Mr Klein warned that no decision would be taken on the scale or shape of US involvement until West African nations got their troops on the ground:
"We need Ecowas to move quickly... Ecowas units should be ready because the Americans will not make their decision until the Ecowas troops are deployed. They're willing to engage. I was very taken by President Bush's commitment to doing something, but they're looking to see now what the region will do first."
He also said Liberia's President, Charles Taylor, would be expected to go into exile - most likely Nigeria - on the day the first American troops arrived.
He expressed hope that Mr Taylor, who has been indicted by a UN-backed international war crimes court in Sierra Leone, would be prevented from meddling in the internal affairs of his country.
Correspondents say rumours of a rebel offensive are preventing Monrovia's displaced population from returning home.
Government officials said Lurd rebels had seized Klay Junction and were advancing towards the city limits.
"We are observing the ceasefire, but the rebels are not," said chief of security, General Benjamin Yeaten.
"We are defending. They are carrying on shelling towards Monrovia."