KHALID ABDELAZIZ and NAFISA ELTAHIR U.N. Secretary-General Antonio Guterres appealed to Sudan's warring factions to observe a ceasefire over the Muslim Eid al-Fitr holiday to allow civilians to reach safe areas as rival forces battled for a sixth day. Thousands of civilians streamed out of the capital Khartoum as gunfire and explosions sounded. Large numbers also crossed into Chad to flee fighting in the western region of Darfur. The United States said it was sending more troops to the region in the event that it decided to evacuate its embassy in Khartoum. Guterres and senior officials from the U.S., Saudi…