[Posted at 11:08 a.m. ET] United Nations Secretary-General Ban Ki-moon on Tuesday congratulated Libya's National Transitional Council Chairman Mustafa Abdel Jalil on the apparent success of the Libyan revolution.

"For Libya this is a historic today," Ban said, directing the new Libyan flag to be presented alongside the United Nations flag.

The move drew a standing ovation from those in attendance.

[Posted at 7:53 a.m. ET] National Transitional Council fighters entered the Libyan city of Sabha Tuesday, long regarded as a pro-Moammar Gadhafi enclave.

The rebel fighters have received no resistance so far in the southern city, according to a CNN team accompanying the NTC forces.

[Posted at 7:52 a.m. ET] An audio message purported to be from deposed Libyan leader Moammar Gadhafi said his political system represented the people's will and could not be overthrown.

The message was broadcast Tuesday on Al-Rai TV, a Syrian-based, pro-Gadhafi television station.

This comes as troops loyal to Libya's new leaders are planning a major assault on Bani Walid, one of the few towns still held by Gadhafi loyalists, a National Transitional Council spokesman there told CNN Tuesday.

"Our fighters are planning a massive attack today to bring the siege to an end," Abdallah Kenshil said.

But the message said Gadhafi supporters are mocking the belief that the longtime ruler and his government can be overthrown.

"This wonderful system is impossible be overthrown," the speaker said. "There is a regime that is being forced on the Libyan people by air and naval bombardment. This is a joke, and its legitimacy is hanging in the air, tied up with bombs and NATO planes that will not last. "

The NTC says forces loyal to the deposed Libyan leader are creating a humanitarian disaster in Bani Walid.

Col. Ahmed Bani told reporters Monday that Gadhafi forces are robbing food stores, leaving civilian residents to starve. He also charged that Gadhafi loyalists are shooting everyone trying to join the revolution, including men, women and children. "They are carrying out mass killings," said Bani, the NTC military spokesman.

"This proves they are trying to destroy the town before it is liberated," he added, calling the Gadhafi forces "criminals" and "killers."

Asked by CNN why, if there is such a humanitarian disaster, NTC forces do not immediately enter the city, the colonel said the problem is "geography." There are tactics the forces must follow to reduce casualties, he said.

Bani Walid is surrounded by anti-Gadhafi forces, he said.

[Posted at 7:00 a.m. ET] An audio message purported to be from deposed Libyan leader Moammar Gadhafi said his political system represented the people's will and it could not be overthrown. The message was broadcast on a Syrian based, pro-Gadhafi television station Tuesday.

This story is developing. We'll bring you the latest information as we get it.