Omar Abdirashid Sharmarke, Somalia's prime minister, has resigned after a prolonged dispute with Sheikh Sharif Ahmed, the country's president. Sharmarke said on Tuesday he "resigned as the prime minister of the transitional federal government of Somalia after being unable to work with the president". The federal government has failed to end a three-year insurgency by hardline Muslim fighters who now control much of the capital and huge chunks of south and central Somalia.