Forces loyal to Muammar Gaddafi have killed at least 25 anti-government fighters on the frontline between Ajdabiya and Brega in eastern Libya, according to rebel sources.
The rebels have spent months trying to seize the strategic oil hub of Brega, which would open the road to Sirte, the Libyan leader's home town, and from there to the capital Tripoli.
"Our men were tricked. Gaddafi's soldiers pretended to surrender, coming with a white flag, and then they fired on us," Mussa al-Mograbi, a rebel commander, told the AFP news agency on Monday.
Dozens more fighters were wounded and transferred to a hospital in Ajdabiya, 160km south of Benghazi, the de facto capital of rebels who have been fighting to overthrow Gaddafi since mid-February.