Rebels said they suffered heavy losses in eastern Libya after being "tricked" by Moamer Gaddafi's forces, as the US pressed Africa to take tougher action against the strongman's regime.
The rebels meanwhile gained another diplomatic boost when Germany recognised their National Transitional Council (NTC) as the "legitimate representative" of the Libyan people.
On the battlefield however, the insurgents came under attack on numerous fronts by Kadhafi loyalists amid a surge of fighting across the country after weeks of stalemate.
On the eastern frontline between the rebel-held transport hub Ajdabiya and the oil town of Brega, which is in the hands of Kadhafi's soldiers, a firefight on Monday left 21 rebel combatants dead, their commander told AFP.
"Our men were tricked. Kadhafi's soldiers pretended to surrender, coming with a white flag, and then they fired on us," Mussa al-Mograbi said.
About 20 rebels were wounded and transferred to hospital in Ajdabiya, 160 kilometres (100 miles) south of Benghazi, the de facto capital of rebels who have been fighting to overthrow Kadhafi since mid-February, he said.
Mograbi added that four of his men were killed and 30 wounded in a skirmish the previous day.
Battles were also being fought in the western town of Zintan, the Berber mountains southwest of Tripoli, in nearby Yafran, and at Dafnia near Misrata, Libya's third city, rebel sources told AFP.
An AFP correspondent said Kadhafi's forces pounded the outskirts of Zintan on Sunday, killing at least seven rebels and wounding 49.
In Addis Ababa, US Secretary of State Hillary Clinton on Monday pressed all African states to demand Kadhafi step down and take tougher action against his regime.
Seeking to wrest support from a leader who has helped them financially, Clinton also urged African countries to expel Kadhafi's diplomats and increase their support for the opposition, saying their words and actions can help bring peace to Libya.
"I urge all African states to call for a genuine ceasefire and to call for Kadhafi to step aside," the first US chief diplomat to speak to the African Union said during a visit to the body's headquarters in Addis Ababa.
Senegal and Gambia are the only African states to have recognised the NTC as the legitimate interlocutor of the Libyan people.
In Benghazi on Monday, German Foreign Minister Guido Westerwelle said after meeting rebel leaders that Germany now recognises the NTC as the "legitimate representative" of the Libyan people.
"We want a free Libya, in peace and democracy without Kadhafi," he added.
Berlin abstained from a UN Security Council resolution vote on March 17 backing intervention in Libya and chose not to join the NATO-led air war, but Defence Minister Thomas de Maiziere said last week it would be ready to consider sending peacekeeping troops to Libya if and when Kadhafi falls.
In Amman, NTC chairman Mustafa Mohamed Abdel Jalil told reporters Germany's recognition "will definitely boost international support for the Libyan revolt."
"Such political gains are key to the revolt and prove that Kadhafi's regime has finished," he said.
Libya's foreign ministry however denounced the visit as a "violation" of Tripoli's sovereignty.
Condemning the visit as "irresponsible", the ministry said it represented "a flagrant violation of national sovereignty, an interference in the internal affairs of a sovereign nation and member of the United Nations, and is contrary to international norms and convention."
In a statement issued in Tripoli, the ministry said such a trip "does not help efforts by regional and international organisations to find a peaceful solution to what is happening in Libya."
Kadhafi remains adamant he will not step down, according to the head of the World Chess Federation Kirsan Ilyumzhinov, who said that during a game of chess in Tripoli on Sunday the strongman insisted he had no position of power to relinquish.
"I am neither premier nor president nor king. I do not hold any post in Libya and therefore I have no position which I should give up," Ilyumzhinov quoted Kadhafi as telling him.
In Tripoli, the regime spokesman said its forces had eliminated rebel "pockets of resistance" at Zawiyah west of the capital.
Mussa Ibrahim told reporters Kadhafi's forces had "total control" of the area from Ajdabiya in the east to the Tunisian border in the west.
In London, the head of the Royal Navy said Britain could have to make tough choices about its military priorities if the Libya campaign drags on.
Admiral Mark Stanhope, the First Sea Lord, said Britain might have to rethink its priorities if the operation went on longer than six months.