Pro-government forces in Libya have shelled rebel fighters near Ajdabiya, challenging the rebels' hold on the city.
The attacks Saturday forced rebels to retreat, slowing their westward advance toward the oil town of Brega on the Mediterranean Sea.
Brega has gone from regime to rebel control and back again several times since the start of an uprising against the government of Libyan leader Moammar Gadhafi.
Meanwhile, the Red Cross says a ship carrying medical supplies has docked in Misrata, a town that has been besieged by pro-Gadhafi forces for weeks. It is the only city in western Libya where rebels have been able to maintain control.
Some information for this report was provided by AP, AFP and Reuters.