|Tony Birtley reports on the thousands who have disappeared from Misurata
Fresh attacks have taken place in central Tripoli, with a series of explosions reported as NATO continues sporadic bombing of the Libyan capital.
A series of explosions and and gunfire was heard across Tripoli in the early hours of Friday morning, according to witnesses.
Footage captured by AP Television showed smoke rising from the city skyline following at least one large explosion.
A Libyan government official, speaking on condition of anonymity to the AP news agency, said that at least 10 NATO raids hit targets in and around Tripoli.
NATO earlier confirmed that it carried out attacks on Thursday, which it said hit military vehicles and ammunition depots, a surface-to-air missile launcher and a fire-control radar.
The attacks took place just hours after NATO and its partners said it would extend the Libyan mission for 90 more days in support of the uprising against Muammar Gaddafi's four-decade rule.
"This decision sends a clear message to the Gaddafi regime: We are determined to continue our operation to protect the people of Libya," Anders Fogh Rasmussen, the NATO secretary-general, said.
Now in its fourth month, the Libyan conflict is deadlocked, with the opposition forces unable to break out of their strongholds and advance towards Tripoli, where Gaddafi appears to be firmly entrenched.
Opposition forces control the east of Libya around Benghazi, the third-biggest city, Misurata, and a mountain range stretching from the town of Zintan, 150km south of Tripoli, towards the border with Tunisia.
On Wednesday, opposition fighters in the country's west said they had managed to force Gaddafi troops out of the towns of Qasr el-Haj and Shakshuk.The towns had been under attack since February.
Residents and opposition forces in the west celebrated on the streets after a battle that lasted for nearly 12 hours.
By liberating the two towns, the opposition says it will now be able restore electricity to three other areas, one of which is Zintan, which has been heavily bombarded in recent days.
In Misurata, opposition fighters have pushed forces loyal to Gaddafi out of the centre of the city and pushed westwards towards the neighbouring town of Zlitan, where they are exchanging artillery fire.
"[Pro-Gaddafi forces] are randomly bombarding from an area near Zlitan," Youssef, an opposition spokesman, told the Reuters news agency from Misurata.
Zlitan could become the next battleground, opposition forces said.
|Opposition fighters say they have forced Gaddafi troops out of two towns in the west [Al Jazeera]
Residents there said pro-Gaddafi forces have been moving into the town and mounting a crackdown to prevent regime opponents from rising up and joining the opposition.
"Gaddafi has tightened security here. His brigades have been getting reinforcement every day. They have stepped up their campaign to arrest, terrify and frighten residents," an opposition spokesman in Zlitan, who identified himself as Mabrouk, said.
"The humanitarian situation is very bad. There are shortages of foodstuffs, baby milk and medicine. There has been no fuel for almost two months."
In another development, UN and US officials said that Qatar deported Iman al-Obeidi, a Libyan woman who accused Gaddafi's soldiers of raping her on March 26, back to Libya.
Vincent Cochetel, the UNHCR representative in Washington, told the AFP news agency that a Qatari military jet flew al-Obeidi to the port city of Benghazi, which is held by rebels, and she was now staying there in a hotel.
A Libyan rebel official told AFP last month that al-Obeidi had escaped from Libya to Qatar with the help of rebels.
She attracted international media attention when she stormed into the Rixos hotel on March 26, threw open her coat to reveal scars and bruises on her body to expose her ordeal.
A UN inquiry accused Gaddafi's government on Wednesday of carrying out systematic attacks on the population, saying it committed war crimes and also crimes against humanity.
While it noted fewer reports of violations by the opposition, the commission of inquiry set up by the UN Human Rights Council also found that rebel forces committed acts that constituted war crimes.
Separately, the Libyan government announced it will send a representative to the meeting of the international oil-exporting countries' group, OPEC, a day after Shokri Ghanem, the country's oil minister, confirmed his defection.
Mussa Ibrahim, the Libyan government spokesperson, said on Thursday that the government would be represented at the meeting of the Organisation of Petroleum Exporting Countries (OPEC) in Vienna on June 8.
"I don't have a name yet, but we'll have somebody," he said.
The announcement came a day after Ghanem announced in Rome that he now supports the Libyan opposition, making him the second most senior official to quit the Gaddafi government.
However, Ibrahim played down the significance of Ghanem's departure. "This is a country, a state, a government, not just one person," Ibrahim told the Reuters news agency.
Up to now, oil and gas has accounted for 95 per cent of Libya's export income, 25 per cent of its gross domestic product and 80 per cent of government revenue, according to US government statistics.