Details added (first version posted at 15:36)
Libyan rebels entered the key eastern city of Ajdabiya on Monday, as the United Nation's special envoy called for an end to hostilities in the western port city of Misurata, dpa reported.
Rebel forces entered the city after coming under heavy ground attack from Libyan armed forces for days on the outskirts of the city Sunday, while trying to recapture the nearby key oil port of Brega, broadcaster Al Jazeera reported.
The rebels have been engaged in fierce fighting with Moamer Gaddafi's military in their bid to advance westwards to the capital Tripoli. They have however failed to secure control of the western port of Misurata, which is seen as a gateway to Tripoli and its surrounding towns.
Speaking from the rebel stronghold city of Benghazi in the east on Monday, a United Nations delegation called for an immediate end to hostilities in Misurata.
The call from UN's top humanitarian official, Valerie Amos, came as local medical staff in Misurata said a further 20 people were killed on Sunday.
Amos said she is "deeply concerned" about the ongoing conflict in Misurata, and in other parts of the country.
"We condemn the tactics used and have raised the issue of cluster munitions with the government in Tripoli," she said.
Amos spoke after visiting Tripoli, where authorities agreed to allow the UN Office for the Coordination of Humanitarian Affairs to set up a presence and distribute humanitarian aid.
The US-based Human Rights Watch (HRW) said Monday that rocket and mortar attacks on residential areas in Misurata may amount to possible war crimes.
"Firing indiscriminately into civilian areas is a clear violation of the laws of war," said Peter Bouckaert, HRW emergencies director.
HRW said cluster munitions as well as Soviet-designed Grad rockets were being deployed by Gaddafi's forces on residential areas. At least eight civilians queuing for bread and were killed and four civilians were wounded in such attacks, the organization said.
HRW also urged Libya's rebels to avoid using unguided Grad rockets seized from Gaddafi's forces.
Misurata has been under attack for some two months, with rebels saying at least 1,000 people have been killed.
Meanwhile, authorities in Egypt on Monday said hundreds of Egyptians were trapped in Misurata. Cairo has been trying for weeks to obtain permission enter to evacuate its nationals. Tripoli has however reportedly said it cannot guarantee the port's safety.
In Benghazi, a further 1,200 migrant workers were expected to arrive Monday from Misurata onboard a ship sent by the International Organisation for Migration (IOM).
According to the IOM, some 3,500 migrant workers are still trapped at the port.
The British government said Monday it would provide financial support to help with the evacuation of some the migrant workers trapped by the fighting in Misurata.
International Development Secretary Andrew Mitchell made the pledge ahead of talks at the United Nations in New York about the humanitarian situation in Libya.
"I am determined that Britain continues to provide help to those innocent civilians who are caught up in the ongoing violence," said Mitchell.
Saif al-Islam, one of Gaddafi's sons, in an interview with the Washington Post, described the fighters in Misurata as terrorists, drawing parallels with Grozny in Chechnya and Fallujah in Iraq.
"You are not fighting or killing innocent people or civilians, because it is not in the interests of anybody to kill civilians, but the terrorists are there, the terrorists are there," he said.
For its part, NATO said it flew 145 sorties over Libya on Sunday, and that 1,110 strike sorties have taken place since the Western alliance took over March 31 the application of a UN approved no-fly zone.
NATO said it destroyed in the last 24 hours, seven ammunition bunkers near Tripoli and four air defense radars around Misurata.