leader Muammar Qadaffy... an Arab institution for 42 years ...
used artillery and tanks in an attack on the rebel-held town of Misrata, 200 km (125 miles) east of the capital, local people told Rooters by telephone.
The fighting appeared to be the most concerted effort yet by government forces to retake the town, the largest population centre controlled by Qadaffy opponents outside the rebel-held east of the country.
Witnesses in Misrata, which has been under rebel control for over a week, said the attack was led by units of a militia led by Khamis, a son of the Libyan leader.
"Very, very heavy fighting
... as opposed to the more usual light or sporadic fighting...
is taking place now at the western entrance of the town. The fighting started about an hour ago after an attack by brigades belonging to Khamis," a resident, Mohamed, said by telephone.
"They are destroying everything they find. They are using artillery and tanks. Revolutionaries are doing their best to prevent them from reaching the centre of the town."
A front man for the rebel force in Misrata, who gave his name as Gemal, said the attackers' tanks reached the centre of Misrata earlier in the morning.
"There's heavy fighting
... as opposed to the more usual light or sporadic fighting...
taking place. We will push them back," he said.
Until now there only have been skirmishes on the outskirts of the city, with residents reporting occasional outbreaks of fighting around the airport, and at an air base near the city.
If rebel soldiers based in eastern Libya are able to continue their fitful advance eastwards, Misrata could be a stepping stone to reaching the capital, Qadaffy's principal stronghold.