Libyan leader Muammar Gaddafi said that his forces would fight a "decisive battle" on Thursday to recapture rebel-held Misrata, the country's third city, in comments broadcast on state television.
"The battle starts today (Wednesday) at Misrata and tomorrow, that will be the decisive battle," said Gaddafi, state television reported.
"From this evening, you are going to be called to take up arms and tomorrow (Thursday) you will take part in the battle," he added, addressing a group of young people from Misrata, the report said.
Gaddafi urged his audience "not to leave Misrata hostage in the hands of a handful of madmen."
Misrata, the country's third city, has a population of half a million people. It lies 150 kilometres (90 miles) from the capital Tripoli.
A rebel spokesman in Misrata said on Wednesday that loyalist forces had launched an attack the city, killing at least four people and wounding 10.
"The city is under attack from all sides but the rebels are still in control and succeeded in capturing two tanks coming in from the south," the spokesman reached by telephone said.
They had succeeded in repelling the attack, he added.