Forces loyal to Colonel Gaddafi launched another attack on the rebel-held city of Misrata in western Libya.
A spokesman for the rebel fighters told Reuters that at least 12 of their men had been killed in the shelling and 26 had been wounded.
Some reports suggested the casualties were sustained when the rebels tried to advance further west towards Tripoli.
Dozens of Gaddafi loyalists are also reported to have been killed in the fighting.
The Libyan government had not commented on the reports by 1830 CET on Wednesday.
The city was the scene of a two-month siege until mid-May when rebels managed to drive government loyalists out.
Medics took the wounded by ambulance for treatment at Misrata hospital. Doctors there called on local people to donate blood.