UNITED NATIONS (AFP) - Sudan has failed to keep a commitment to withdraw its forces from the disputed territory of Abyei by Friday, a UN spokesman said. "To our knowledge that withdrawal has not taken place," UN spokesman Martin Nesirky said, making a new appeal to Sudan and South Sudan to withdraw their troops from the flashpoint region on their tense border. "We have urged the parties to implement the agreement they reached earlier this month and to withdraw their forces from the Abyei area so as to facilitate the return of the displaced population and ensure the smooth beginning of the migration season."