Opposition leaders say they arrested dozens of armed men loyal to Muammar Gaddafi in their eastern bastion, but have suffered a blow in Libya's west, losing a village at the foot of a key mountain range.
At least 63 people suspected of having links to Gaddafi, and of murdering the rebels' military chief, were rounded up by the rebels, following an hours-long battle in the opposition stronghold of Benghazi.
Security forces patrolled the streets overnight and on Monday in a bid to track down more members of the pro-Gaddafi group, a rebel spokesman said.
Opposition forces captured the base of the Gaddafi loyalists, called the al-Nidaa Brigade, an armed group which had been operating under the opposition's banner, spokesman Mahmoud Shamam said.
Medics said at least four opposition members and 11 pro-government troops were killed in the clashes.
Al Jazeera's Tony Birtley, reporting from Benghazi, said the battle was launched to subdue elements of Gaddafi's forces that had been operating as a "fifth column" within the opposition ranks.
He said that documents had been found at the base that linked the brigade to Gaddafi.
"We caught about 38 and later today more than 25," Mustafa el-Sagisli, the rebels' deputy interior minister, told the AFP news agency late on Sunday, referring members of the al-Nidaa Brigade who were rounded up for allegedly organising a prison break in Benghazi earlier in the week.
"Some of them ran away and we are trying to catch them all over the city," el-Sagisli said. "We are arresting them."
Ismail al-Salabi, who heads military operations for February 17 Martyrs Brigade, a faction within the rebels, called the operation "100 per cent successful" and added the rebels seized explosives and several pickup trucks equipped with machine guns.
The fighting followed Thursday's killing of Younes, the chief rebel commander, under mysterious circumstances.
El-Sagisli said the al-Nidaa Brigade had been involved in "plans to [plant] car bombs" and that they had "participated in many acts of terrorism inside Benghazi".
He also said the "very same group" of fighters was suspected of involvement in the assassination of Younes, who was a right-hand man to Gaddafi before his defection to the opposition.
Birtley reported that while the fighting in Benghazi was indicative of unease, it did not mean that strong divisions yet existed in the rebels' ranks.
"I'm not sure there are huge divisions, but there are some cracks. The [opposition National Transitional Council] is taking great steps to suggest their unity is intact and they are speaking with one voice," he said.
Forces loyal to Gaddafi, meanwhile, took control on Monday of the village of al-Jawsh at the foot of the strategic western Nafusa mountains, AFP journalists at the scene said.
The rebels had on Sunday taken the village, but said they were forced to retreat to the east, half way along the road to the town of Shakshuka, after several hours of fighting.
The rebels said al-Jawsh had been emptied of residents and pro-Gaddafi forces were now in the village.
The Nafusa region has seen heavy fighting between rebels and forces loyal to Gaddafi since the rebels launched a major offensive this month in a drive on the capital Tripoli.
Fighting was also reported near the eastern oil town of Brega, where rebels say they are advancing on pro-Gaddafi troops stationed there.
Several explosions were also reported to have taken place an eastern district of the capital, Tripoli.
Migrants 'dead in transit'
On the diplomatic front of the conflict, France announced on Monday that it had released $259 million in frozen funds to the NTC.
"These are funds that belong to the Libyan people" and will be used to buy "food and medicine", said Mansour Seyf al-Nasr, the Libyan opposition's new ambassador to Paris, after meeting with Alain Juppe the French foreign minister.
In Italy, 25 men who were apparently fleeing the violence in Libya were found dead in a small boat that arrived at the island of Lampedusa on Monday, port authorities said.
The men appeared to have been asphyxiated by motor fumes while on board.
The boat arrived after a three-day voyage from Libya, and was carrying at least 271 people from sub-Saharan Africa, including 36 women and 21 children.
"Twenty-five bodies were found on board a boat from Libya; the others appear to be fine, they are now undergoing checks," said Antonio Morana, the commanding officer at Lampedusa port.
Local prosecutors have opened an investigation to ascertain whether any criminal responsibility can be established under laws against aiding clandestine immigration.