Leaders of the peacekeeping operation want Liberia's main rebel group, LURD, to open the seaport to allow the distribution of emergency food and medical aid.
A convoy from the International Committee of the Red Cross and Doctors without borders was allowed into rebel territory on Friday. It was the first time relief agencies have crossed Monrovia's front lines in weeks.
Two months of fighting in and around Monrovia have devastated the city. About two-thousand people have been killed and hundreds of thousands of others stranded inside the capital without clean water, food and proper sanitation. Some aid has been flown into Liberia, but the majority of aid must come by ship.
LURD rebels have said they would withdraw from their positions in Monrovia once the peacekeeping force arrived. But they now appear reluctant to do so until President Charles Taylor resigns and leaves Liberia, as he has promised.
Elsewhere in Liberia, the rebels accuse government forces of attacking their positions in the town of Arthington, 20 kilometers northwest of Monrovia.
On Thursday, a convoy of Nigerian peacekeepers patrolled Monrovia for the first time. Tens of thousands of war-weary civilians lined the streets, cheering the troops on and chanting " We want peace!"
About 450 Nigerian soldiers flew into Liberia this week, the first units of what will be a 32-hundred-strong West African peacekeeping force. The troops were sent to enforce a ceasefire and facilitate the distribution of humanitarian assistance.