UN Secretary-General Ban Ki-moon on Wednesday called on all parties in the Libyan conflict to "accept an immediate cease-fire," saying that "those responsible for the continuous use of military forces against civilians will be held accountable."

"The secretary-general is gravely concerned about the increasing military escalation by government forces, which include indications of an assault on the city of Benghazi" in the eastern part of the North African country, Ban's spokesman Martin Nesirky told reporters here. "A campaign to bombard such an urban center would massively place civilian lives at risk."

"The secretary-general is urging all parties in this conflict to accept an immediate cease-fire and to abide by Security Council Resolution 1970," Nesirky said. "Those responsible for the continuous use of military forces against civilians will be held accountable."

The secretary-general made the statement as the UN Security Council is meeting behind closed doors to discuss the issue of a no-fly zone over Libya, a move endorsed by the Arab League in its decision reached at the end of an emergency meeting on Sunday.

"The secretary-general has remained closely abreast of the situation in Libya and the critical discussions under way in the Security Council over measures aimed at protecting civilians," Nesirky said.

Ban spoke by phone on late Tuesday with Libyan Foreign Minister Mussa Kussa, the spokesman said, but he did not disclose the details of the phone conversation between the Libyan minister and the secretary-general, who is on his visit to Guatamala on Wednesday.

"The secretary-general's special envoy, Mr. Abdul Ilah Khatib, has departed Libya today with his delegation after two days of discussions in which he conveyed to senior Libyan officials the strong calls by the international community to cease the fighting and the violence, to ensure humanitarian access and to work toward a peaceful solution of the crisis," Nesirky said.

"The special envoy stressed the need for a firm and unambiguous commitment on the part of the Libyan government to cease hostilities immediately," he said. "The special envoy's efforts continue, including contacts with representatives of Libyan political groups in Benghazi, as well as with the authorities in Tripoli."

Forces loyal to Libyan leader Muammar Gaddafi have launched a major attack on the rebel-held city of Misurata, 200 kilometers east of the Libyan capital of Tripoli, killing at least five people, Al-Jazeera TV reported on Wednesday.

Wednesday's attack came as Gaddafi's forces prepared to push further towards the rebel stronghold of Benghazi in the country's east. Libyan government forces loyal to Gaddafi recaptured the eastern town of Ajdabiya on Tuesday, the Libyan state TV reported.

Inspired by streets-born protests which had swept Tunisia and Egypt and forced their leaders to step down, thousands of Libyans have started a string of protests against Gaddafi, who has been in power for 42 years.