UNITED NATIONS -- The U.N.'s deputy emergency relief coordinator said Thursday that three-quarters of Libya remains cut off from humanitarian assistance as international concern mounted about the lack of access to areas of heavy fighting.

Catherine Bragg told more than 100 diplomats at a briefing on the Libyan crisis that the United Nations is urgently working to establish dialogue with all parties to gain access to all areas of the country and assess the humanitarian needs of civilians.

Secretary-General Ban Ki-moon got an initial green light over the weekend from Libyan Foreign Minister Musa Kusa to send a U.N. team to assess humanitarian conditions and followed up Wednesday to try to speed up arrangements, she said.

Bragg said Ban's new special envoy to Libya, Abdelilah Al-Khatib, and the U.N.'s new humanitarian coordinator for Libya, Rashid Khalikov, will travel to Tripoli, possibly this weekend. She said the U.N. is preparing humanitarian assessment teams to be deployed as soon as possible.

"Inside Libya, we have scanty information on the humanitarian fallout from the intense fighting in the past few days," Bragg said. "Medical needs are a major concern, particularly as we are receiving reports of hospital closures at a time when people most need medical care. We need nurses, and wounded civilians need to reach these facilities."

Red Cross President Jakob Kellengerger said in Geneva that "it's unacceptable that, 24 days after the fighting started, a major part of the country remains effectively cut off from humanitarian aid."

"Our greatest challenge right now is to reach the areas hardest hit by the fighting in order to help treat the war-wounded and follow up on people who have gone missing, as we've been doing in the east of the country since we arrived on Feb. 27," he said.

Kellenberger said local doctors over the past few days saw a sharp increase in casualties arriving at hospitals in Ajdabiya, in the rebel-held east, and Misrata, in government territory.

He said "reliable sources" reported that 40 patients were treated for injuries, some very serious, at a medical facility in Misrata, and that 22 bodies were taken there. He said a Red Cross surgical team in Ajdabiya helped operate on some of the 55 wounded people brought to the city's hospital this week.

"This is but one sign that the conflict is intensifying," Kellenberger said. "Our concern is that civilians are bearing the brunt of the violence. We believe that many people in western Libya have been even more severely affected by the fighting than those in the east."

Libya's deputy U.N. ambassador Ibrahim Dabbashi, who has demanded Gadhafi's ouster, told the diplomats: "Now is the right time to assist the Libyan people, whether on the humanitarian level or the military level, because we are confronting a regime that shows no mercy, that does not recognize international law and does not recognize humanitarian morality."

Dabbashi said those injured in fighting in Misrata and Zawiya can't be moved to hospitals in neighboring villages because the Gadhafi government has closed them. Zawiya is the city closest to the capital, Tripoli, that fell into opposition hands but may have been retaken by the government.

He said the number of casualties is difficult to determine but "we expect that there are thousands of dead in Tripoli."

Bragg said almost 250,000 people have left Libya, over 137,000 to Tunisia, about 108,000 to Egypt and smaller numbers to Niger and Algeria.

She said the U.N. is especially concerned about the conditions for foreigners remaining in Libya, particularly those from sub-Saharan African "who may fear persecution" and must be allowed to leave the country if they wish.

Gadhafi has reportedly recruited mercenaries from sub-Saharan Africa, which has led to the targeting of black Africans working in the country.

Egypt's U.N. Ambassador Maged Abdelaziz expressed serious concern about the more than one million Egyptians still in Libya, and the small number of foreigners leaving, particularly from the west.

"And we are afraid that the tragic events that happened in Iraq using human shields to protect air defense systems on the ground would be repeated," Abdelaziz said, though he added that Egypt has "no concrete information" about such a possibility.

The U.N. launched an appeal Monday for $160 million to cover projected humanitarian needs for three months and Bragg said $36 million has been contributed.

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Associated Press Writer John Heilprin contributed to this report from Geneva.