Foreign ministers from around the world are meeting in Geneva to discuss their response to the mounting humanitarian crisis in Libya.
Tens of thousands of migrants - many from Egypt - are stranded near Libya's Tunisian border with a thousand new arrivals every hour, UN officials say.
Correspondents say there is an uneasy stalemate, with leader Muammar Gaddafi still very much in control in Tripoli.
The US has publicly backed anti-Gaddafi groups in eastern Libya.
Opening the Geneva meeting, UN Human Rights Commissioner Navi Pillay warned the Libyan authorities that widespread attacks on civilians could amount to crimes under international law.
"It is a matter of great sadness that so much blood has been shed to usher in change. Let me reiterate that the illegal and excessively heavy-handed response of a number of governments is unacceptable," she said.
Speaking on her way to the meeting, US Secretary of State Hillary Clinton said Washington was "reaching out to many different Libyans in the east".
Mrs Clinton said she would discuss co-ordinated responses on both the humanitarian and political fronts with many of her counterparts from Europe, the Middle East and North Africa at the UN human rights council meeting in Geneva.
At least 1,000 people are believed to have been killed in nearly two weeks of violence in which eastern cities have fallen to anti-government forces.
