A member of the Benghazi city council said the Libyan cities under rebel control have appointed an ex-justice minister to lead a provisional government.
Fathi Baja said opponents of Libyan dictator Muammar Gaddafi named Mustafa Abdel-Jalil to the provisional leadership post.
Mr Baja said that Mr Abdel-Jalil was chosen by the committees running the eastern Libyan cities now in the rebellion's hands.
On Saturday, Libya's top envoy to the US also said Gaddafi opponents were rallying behind efforts to form an alternative government led by Mr Abdel-Jalil, who has criticised Gaddafi's brutal crackdown on protesters.
It was not immediately unclear how much support the proposed provisional leadership commands.
The uprising against Gaddafi began in Benghazi on February 15. The rebels now control most of the eastern half of the country.
Earlier today the UN Security Council voted unanimously to impose sanctions on Libyan leader, his five adult children and top associates.
Voting after a day of discussions - interrupted at times for consultations with home capitals - council members agreed to freeze the assets of Mr Gaddafi, his four sons and one daughter, and to ban travel by the whole family plus 10 close associates.