Four rebels were killed and 22 wounded in overnight clashes against forces loyal to Libyan leader Muamer Gaddafi in the western town of Zliten, rebels said on Monday.
Rebels were advancing to the centre of Zliten, 60 kilometres (36 miles) from their western coastal enclave of Misrata, Libya's third city, they said in a statement.
The clashes flared in Souk al-Thulatha district near the centre of Zliten, a strategic gateway town for the rebels seeking to march on to Tripoli, 200 kilometres (125 miles) further east.
"Four of our fighters were martyred and another 22 were gravely injured in clashes with loyalist forces," the statement said. Kadhafi's forces had used "heavy weapons and cluster bombs banned by international conventions."
In west Libya, rebels are fighting Kadhafi's forces on two fluid front lines: in and around the Mediterranean coastal town of Zliten and hamlets of the Nafusa mountain range, west of the capital.