The country's leader of 41 years labelled his international opponents "fascists", calling the conflict an "historic battle" against "unjust aggression".
US President Barack Obama has ruled out a land invasion of Libya.
But the American military warned it was considering all options in response to dire conditions for residents of the coastal area of Misratah.
People there say they have been left cowering in darkened homes and scrounging for food and rainwater.
A doctor, speaking on condition of anonymity for fear of reprisals if the city falls to Col Gaddafi's troops, said tanks had opened fire on a peaceful protest.
"The number of dead are too many for our hospital to handle," he said. Read More