|Rebels battling Gaddafi's forces estimate that up to 5,000 government troops are defending Brega [Reuters]
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.
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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.
Brega boasts an important oil refinery which, once operational, could supply the east of the country with much-needed fuel to produce electricity.
French and British attack helicopters have been backing rebels by targeting positions of pro-Gaddafi forces in and around Brega since June 3.
Rebels, who refuse to specify how many fighters have joined their ranks, estimate that up to 5,000 loyalist troops are defending Brega.
Battles between pro-democracy fighters and Gaddafi forces continued across the west of the country, as rebels said they were advancing towards Tripoli.
Rebel fighters said they were making gains towards Zlitan from the port city of Misurata - which is under their control. Zlitan is one of three towns separating Misurata from the capital Tripoli.
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Battles were also being fought in the Berber mountains southwest of Tripoli, in nearby Yafran, and at Dafnia near Misurata, Libya's third city, rebel sources said.
An AFP correspondent said Gaddafi's forces pounded the outskirts of Zintan on Sunday, killing at least seven rebels and wounding 49.
Government forces posted a few miles east of Zintan, which remains under rebel control, fired Grad and Katyusha rockets at the town.
NATO, which has been bombing Gaddafi forces since late March, said it was taking "necessary action" to protect civilians.
"NATO is monitoring the situation closely and is taking necessary action to protect civilians," a statement by the Western alliance said.
"Along the north-west coast of Libya between Tripoli and the Tunisian border Libyans long tired of Gaddafi rule are challenging his legitimacy openly, and in doing so, are under threat of attack."
On the diplomatic front, international support of the rebels grew on Monday with Germany becoming the latest nation to endorse Libya's opposition.
The recognition, voiced by Guido Westerwelle, the German foreign minister, on a visit to Benghazi is significant because Germany has been reluctant to be drawn into the Libyan conflict and opted out of NATO military action.
"We share the same goal - Libya without Gaddafi," Westerwelle announced in Benghazi after meeting members of the rebel Interim National Council (INC).
Countries that have recognised the INC include France, Italy, Qatar and the United Arab Emirates.
For her part, Hillary Clinton, the US secretary of state, urged African leaders to follow suit and abandon Gaddafi.
"It has become clear that we are long past the time when he [Gaddafi] can remain in power," she said in a speech to the African Union at its headquarters in the Ethiopian capital, Addis Ababa.
"Your words and your actions could make the difference ... in ending this situation and allowing the people of Libya to get to work writing a constitution and rebuilding their country," she said.
Source: Al Jazeera and agencies