"We are working to ascertain the facts, but we have received multiple credible reports that hundreds of people have been killed and injured in several days of unrest and the full extent of the death toll is unknown due to the lack of access of international media and human rights organizations," a State Department spokesman said.

"We have raised to a number of Libyan officials, including Libyan Foreign Minister Musa Kusa, our strong objections to the use of lethal force against peaceful demonstrators. We reiterated to Libyan officials the importance of universal rights, including freedom of speech and peaceful assembly,' P J Crowley said in a statement.

"Libyan officials have stated their commitment to protecting and safeguarding the right of peaceful protest.

We call upon the Libyan government uphold that commitment, and hold accountable any security officer who does not act in accordance with that commitment," the spokesman added.