Battles between pro-democracy fighters and forces of Muammar Gaddafi, the Libyan leader, are continuing across the west of the country, as rebels say they are advancing towards the capital.
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.
The opposition said it had also fought street by street to retake the Mediterranean port city of Zawiyah, a major oil port 50km west of Tripoli.
Libya's government said it had stopped opposition fighters from entering Zawiyah, but rebels said on Sunday they were continuing to fight for the town after hours of battles.
Thirteen people were reported killed in clashes in Zawiyah.
Rebels said they had taken control of a large area in the town's west.
The rebels on Sunday said they had lost at least four killed in fighting between Brega and Ajdabiya.
At least 65 fighters were wounded, doctors at the hospital in the rebel stronghold city of Benghazi said.
Mussa Ibrahim, the government spokesman, said that Gaddafi's forces had "total control" of the area from Ajdabiya in the east to the Tunisian border in the west.
"It is pockets of resistance. The rebels there are no more than a hundred. The army has killed some of them, captured others and is negotiating the surrender of others," he said.
"The wishful reporting of some journalists that the rebels are gaining more power and more control of some areas is not correct."
The rebel thrust at Zawiyah and reported movements farther east - near Misurata and the oil port of Brega - suggested the stalemated uprising had been reinvigorated.
Rebels launched an offensive on Sunday to retake the oil town of Brega, but they were repelled in a battle which killed at least four fighters and wounded 25, rebels and doctors said.
An AFP correspondent said Gaddafi's forces had pounded the outskirts of opposition-held Zintan on Sunday, killing at least seven rebels.
Government forces, posted a few kilometres east of Zintan, fired Grad and Katyusha rockets at the town.
Doctors at Misurata's Hikma hospital said on Sunday that six people were killed in shelling of the contested western city and 16 more were wounded. But Zintan remains in rebel hands.
Rebel fighters said they had captured 10 prisoners from Gaddafi's forces and destroyed a number of vehicles in southern Misurata.
The developments came as NATO said it was taking "necessary action" to protect civilians west of Tripoli because they were under threat of attacks for openly challenging the regime.
"NATO is monitoring the situation closely and is taking necessary action to protect civilians," a statement said.
"Libyans long tired of Gaddafi's rule are challenging his legitimacy openly, and in doing so, are under threat of attack."
No plans to stand down
Elsewhere, Libyan state television broadcast pictures of Gaddafi meeting Kirsan Ilyumzhinov, the Russian head of the International Chess Federation.
Russia's Interfax news agency quoted Ilyumzhinov as saying he played a game of chess in Tripoli with Gaddafi, who said he had no plans to stand down or leave his country.
"Gaddafi stated that he is not going to leave Libya, stressing that it is his motherland and a land where his children and grandchildren died," Ilyumzhinov told Russia's Interfax news agency.
In another development on Sunday, the United Arab Emirates (UAE) said it had recognised the Libyan rebel council as the sole legitimate representative of the Libyan people.
"This recognition affirms that the UAE is committed to maintaining strong ties with the Libyan people," Abdullah bin Zayed Al Nahyan, the UAE foreign minister, said in a statement carried by WAM, the state news agency.
Al Nahyan said the UAE would open a representative office in the opposition stronghold Benghazi soon.
Earlier, the council had won full recognition from Spain, France, Italy, Qatar and Jordan, while the US has invited the rebels to open an office in Washington.