Fathi Baja, member of the Benghazi city council, says opponents of Libyan dictator Muammar Gaddafi named Mustafa Abdel-Jalil to the provisional leadership post.
Baja said Sunday that 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 Gadhafi opponents were rallying behind efforts to form an alternative government led by Abdel-Jalil, who has criticized Gaddafi's brutal crackdown on protesters.
It was not immediately clear 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.