Rebels said Gaddafi's forces fired Russian-made Grad rockets, which rights groups say should not be used in civilian areas, at the rebel-held western towns of Misrata and Zintan following NATO strikes to free Misrata's port.

In Zintan, the rebels struck back.

"Rebels attacked posts belonging to Gaddafi forces east of Zintan in the early evening. The posts have been used to fire rockets into Zintan," the spokesman, called Abdulrahman, told Reuters.

"The rebels destroyed at least three tanks and captured two others."

Remoter areas of western Libya also came under fire from forces loyal to Gaddafi, trying to break an uprising against his four-decade rule that has put most of the east in rebel hands since it began in mid-February.

The United States voiced confidence in the Benghazi-based main opposition council Wednesday as the U.S. Treasury moved to permit oil deals with the group, which is struggling to provide funding for the battle-scarred areas under its control.

The order by the U.S. Treasury Department's Office of Foreign Assets Control may help to clear up concerns among potential buyers over legal complications related to ownership of Libyan oil and the impact of international sanctions.

The first major oil shipment from rebel-held east Libya, reported to be 80,000 tons of crude, was expected to arrive in Singapore on Thursday for refueling but oil traders told Reuters finding a buyer was not straightforward, with many of the usual traders still worried about legal complications.

A tanker booked for Italian oil company Eni to carry crude to Italy from Gaddafi-held territory in Libya never arrived in port and left empty last week because the sanctions meant the government would not have got paid, trade sources said.