(Adds minority says to lift gas pipeline halt, another power plant halted)
TRIPOLI, Dec 4 (Reuters) - Many Libyan cities are headed for blackouts in two days unless protesters demanding more political rights end a blockade of fuel supplies to a vital power station, state news agency Lana said.
A group of Tibu, a black ethnic minority, and other protesters have blocked supplies of petrol to a power station in Sarir in southern Libya.
The Sarir power plant, the biggest in southern and eastern Libya, will halt operations within 48 hours unless the Tibu end a road blockade to let badly needed petrol through, the plant's manager Hashim Malik told state news agency Lana.
"This will plunge many cities in Libya into total darkness," Malik was quoted as saying.
In Western Libya, the state power company shut down another plant, also named Sarir, due to labour protests and maintenance work, Lana said. The firm blamed "irresponsible action" by strikers.
Another minority group, the Amazigh, or Berbers, has stopped shipment of gas supplies from the southwestern Wafa field for weeks, but one of its leaders said the blockage would be lifted on Thursday to ease the power outages.
"We are doing this to meet the government demand," Amazigh leader Ibrahim Makhlouf said, adding that details would be unveiled at a news conference on Thursday.
Both groups are demanding that their languages and cultural identities be guaranteed in a new constitution two years after the fall of Muammar Gaddafi. They are also want a greater say in a special body that is drafting the constitution.
Power went off on Wednesday for several hours in parts of the capital Tripoli and the eastern city of Benghazi. Power failures have worsened in the past few days as temperatures have fallen to lows of around 12 degrees Celsius and household demand for heat has risen.
The strikes come on top of widespread protests at oilfields and ports over higher pay and political rights, which have halted most exports and dried up state revenues.
Last week the government said power production had fallen to 4,600 megawatts, less than the summer level of almost 6,000 megawatts, when demand rises for air-conditioning. (Reporting by Ulf Laessing and Ghaith Shennib; Editing by Jane Baird)