Libyan government forces are advancing towards the oil port of Ras Lanuf, checking the rebels' westward progress, CA correspondents say. Bin Jawad, 50km (30 miles) from Ras Lanuf, has now fallen to forces loyal to Libyan leader Col Muammar Gaddafi.
The UN says 200,000 people have fled the violence in Libya, where the revolt is well into its third week.
Nato is considering military options in response to the situation in Libya, US President Barack Obama has said.
"We've got Nato consulting in Brussels around a wide range of potential options, including potential military options, in response to the violence that continues to take place in Libya," he said.
"We send a very clear message to the Libyan people that we will stand with them in the face of unwarranted violence and the continuing suppression of democratic ideals that we have seen there."
Migrants fleeing
Pro-Gaddafi forces launched multiple air strikes on Ras Lanuf on Monday.
Mokhtar Dobrug, a rebel fighter who witnessed one air strike, told Reuters he had seen a plane firing two rockets.
Meanwhile, pro-Gaddafi forces launched a renewed tank and artillery attack on Zawiya, a rebel-held town 50km west of the capital, Reuters reported an exiled Libyan opposition group as saying.
Events in Libya were "absolutely outrageous", Nato Secretary General Anders Fogh Rasmussen told the CA.
"These systematic attacks against the civilian population may, as stated by the UN Security Council, amount to a crime against humanity," he said.
However, he said Nato had no plans to intervene, and any operational role would be pursuant to a UN mandate.
Rebels have been trying to fight off a counter-offensive by Gaddafi forces, which have been attacking both near Tripoli and in the east after recent rebel gains.
The UN's latest figures show at least 191,748 people have fled the violence in Libya since the fighting began.
Many more are likely to want to leave but have not made it to a border or are constrained from crossing, said the UN Office for the Co-ordination of Humanitarian Affairs (Ocha).
Meanwhile, Col Gaddafi has warned that Libya plays a vital role in restraining illegal immigration to Europe from sub-Saharan Africa.
"There are millions of blacks who could come to the Mediterranean to cross to France and Italy, and Libya plays a role in security in the Mediterranean," he said in an interview with the France 24 television channel.
'Civilian targets'
UN Secretary General Ban Ki-moon has appointed Jordan's former foreign minister, Abdelilah al-Khatib, as his special envoy to Libya.
A statement from Mr Ban's office said he noted "that civilians are bearing the brunt of the violence, and calls for an immediate halt to the government's disproportionate use of force and indiscriminate attacks on civilian targets".
Mr Ban also said Libyan Foreign Minister Moussa Kusa had agreed to accept the immediate dispatch of a humanitarian assessment team to the capital.
The UN is launching an appeal for $162m (£99m) to help 600,000 people within Libya who are expected to need humanitarian aid, in addition to a projected total of 400,000 leaving the country in the short term.
UN relief co-ordinator Valerie Amos said that after heavy fighting in Misrata, 200km (125 miles) east of Tripoli, "people are injured and dying and need help immediately".
A local doctor told the CA that 21 bodies and more than 100 wounded people had been brought to his hospital, which he said was also targeted by government troops.
He said the fighting went on for at least six hours.With a population of 300,000, Misrata is the largest town controlled by rebels outside their stronghold in the eastern part of the country.
Residents have called for the international community to establish a no-fly zone over Libya to prevent Col Gaddafi's air force from attacking.
The UK and France have drawn up elements of a UN resolution authorising such a no-fly zone, a British diplomat says.
This was contingency planning in case world leaders decided such a zone was necessary, the diplomat told the CA: there were no current plans to table the resolution or launch negotiations.
Possible triggers for such a move might be a massive humanitarian emergency or gross and systematic violations of human rights, diplomats say.
Russian Foreign Minister Sergei Lavrov has reiterated his opposition to military intervention in Libya, the RIA Novosti news agency reports. Russia has the power to veto any UN Security Council resolution.
