The city was considered one of the key remaining strongholds of fugitive leader Col Muammar Gaddafi's forces.

Nato, whose air-strikes have been vital in bolstering the efforts of anti-Gaddafi forces, said it will extend its air campaign for up to 90 days.

There are also reports of many deaths in Hun, near the desert town of Jufra.

Fierce fighting also continues at other Gaddafi hold-outs Bani Walid and Sirte.

NTC military spokesman Ahmed Bani said: "We control most of Sabha apart from the al-Manshiya district. This is still resisting, but it will fall."

The NTC had said on Monday that its forces had captured the airport and a leading garrison in Sabha, 750km (465 miles) south of the capital, and taken 150 prisoners from the Gaddafi forces.