Ms. Pillay also urged NATO forces to exercise the utmost caution and vigilance so as not to kill civilians by mistake. The alliance has been carrying out air strikes in response to Security Council resolution 1973, which was adopted last month and authorized Member States to take "all necessary measures" to protect civilians in Libya.

"The situation in Misrata grows more serious every day," said UN humanitarian chief Valerie Amos, who has just returned from a two-day mission to Libya during which she visited the capital, Tripoli, and the rebel-held city of Benghazi.

She told a news conference at UN Headquarters that while the UN is unable to obtain verifiable numbers, it is clear that hundreds of people have been killed and wounded during the almost continuous fighting in the besieged city.

During her visit last weekend, the UN and Libyan authorities signed an agreement on ensuring protection for humanitarian aid organizations and granting access to those who need assistance.

"We need humanitarian teams on the ground so that we can get a sense of what is actually happening to assess needs to enable us to plan and respond effectively," said Ms. Amos, the Under-Secretary-General for Humanitarian Affairs and UN Emergency Relief Coordinator.

Specifically, the Government agreed to facilitate the establishment of the humanitarian presence in Tripoli to coordinate the delivery of assistance; to provide the security guarantees necessary for a UN humanitarian presence in areas under the control of the Libyan Government; and to facilitate the entry and the exit of aid workers and the import of all material and equipment necessary to support the UN humanitarian presence in the country.

Ms. Amos said the UN plans to send a team into Tripoli as early as this weekend. This is in addition to humanitarian staff already on the ground in Benghazi, and in Egypt, Tunisia and Niger.

"Our humanitarian efforts are focused on reaching those who urgently need our help," she said.

Also today, the Special Representative of the Secretary-General on Sexual Violence in Conflict, Margot Wallstr?m, said that there is an urgent need to focus on the prevention of sexual violence as the fighting escalates in Misrata and other parts of Libya.

"Despite robust action by the international community to protect civilians in Libya, we still hear reports of sexual violence," said Ms. Wallstr?m, who strongly condemned the use of sexual violence as a means to political and military ends.

"I call upon all parties to allow access for UN staff and humanitarian organizations in order for them to monitor such violations and deliver aid to civilians caught in the fighting," she said in a statement.