Liberians hope the peacekeepers can end the fighting
Rebel leaders in Liberia have accused President Charles Taylor's troops of launching new attacks and have threatened to retaliate.
Their accusations came ahead of a proposed meeting with the United States envoy in Monrovia who is trying to gain approval for Nigerian peacekeepers to enter rebel-held parts of the capital.
A top official of the main rebel group, Liberians United for Reconciliation and Democracy (Lurd), accused Mr Taylor's forces of attacking the town of Arthington, 40 kilometres from the capital.
"We are asking for Taylor to leave Arthington, which is fully under our control, or we will resume fighting," , Sekou Fofana said.
The BBC's Barnaby Phillips in Monrovia says extending the peacekeeping patrols is important because the rebels control the port, where there are supplies of food and fuel.
Access to the port would allow new shipments of humanitarian aid to be delivered to Monrovia's residents.
On Thursday, the Nigerians were given an ecstatic welcome when they began patrols of Monrovia for the first time since their arrival in the country on Monday.
In government areas, there are shortages of water and food, while the many sick and wounded on both sides of the front line need medical supplies.
The rebels have previously said that humanitarian aid can be delivered to the port but they say they will not withdraw from Monrovia until Mr Taylor leaves Liberia.
Aid agencies are also planning to cross the front line for the first time on Friday.
"We are expecting to go to about four places where we know they've been collecting wounded. We want to evacuate emergency cases for surgery," said Jordi Raich, head of the International Committee of the Red Cross (ICRC) mission.
The ICRC has also called on all parties to allow humanitarian aid through, saying the Liberian people had "been neglected to a point rarely seen even in Africa".
"We're starving. We're eating food that humans should not be eating," said 27-year-old Athanasius Carr.
The AP news agency reports that Monrovia residents are eating leaves, small red "monkey fruit" and swamp snails, known as "kiss meat."
On Thursday, Liberian President Charles Taylor sent a letter of resignation to parliament, saying that he would hand over power to Vice President Moses Blah on Monday 11 August.
However, he did not specify when he would leave the country and take up an offer of asylum in Nigeria.
The rebels have said they will not accept Mr Blah as Mr Taylor's successor.
"If Moses Blah takes over, we will fight back. We will definitely fight Moses Blah," said Mr Fofana.
A United Nations-backed war crimes tribunal has issued an international warrant for Mr Taylor's arrest for his alleged role in the brutal 10-year civil war in neighbouring Sierra Leone.
Four weeks of bitter fighting in the capital has greatly eased since the peacekeepers, numbering around 400, started arriving at Robertsfield airport, 40 kilometres from the city centre.
Liberia's defence minister has confirmed reports that West African peacekeepers blocked a shipment of arms destined for Mr Taylor at Robertsfield airport on Thursday.
The plane has now flown on to the Nigerian city of Lagos.