BENGHAZI, Libya, Jan 17 (Reuters) - The speaker of Libya"s eastern-based parliament said on Monday the interim government must be replaced and he would launch a process to redraft the constitution, after plans for an election fell apart last month. The moves, announced by Parliament Speaker Aguila Saleh as he entered the chamber in the eastern city of Benghazi, could delay by months any new election aimed at ending years of war between factions based in the east and the west. An interim Government of National Unity took office last year and national elections were meant to take place on Dec. 24, but the vote was put off amid disputes between rival factions over the rules. There is no agreement yet among Libyan political leaders or foreign powers over what to do next. Saleh said the GNU was no longer legitimate, a new government must be installed, and a new committee be formed to rewrite the constitution. Any new government unilaterally declared by the parliament could thrust Libya back to the division between eastern and western administrations that prevailed before the GNU was installed. Any such moves are likely to be challenged by other Libyan political institutions, and any new disputes over the process could further delay the elections. GNU spokesman Mohamed Hamouda said the administration "works according to a political agreement and a road map" and that it would continue to operate until the elections were held. Western countries have said they will continue to recognise the GNU for now. The U.N. Libya adviser, Stephanie Williams, has said the focus should be on holding elections rather than installing a new interim government. Tarek Megerisi of the European Council on Foreign Relations think tank said foreign powers will probably stick to their calls for elections, backing a new U.N. mediation process to come up with a consensus on new election rules. Since the polling day passed without a vote, rival factions have been negotiating on what to do next. Election commission head Emad Sayeh, who had previously suggested a delayed election on Jan. 24, said it would take 6-8 months to organise any new election that involved a new process for registering candidates.