HEAVY firing rang out in Khartoum after Sudan's army declared a truce, a Reuters witness said, dealing the latest blow to international attempts to try to end almost a week of fighting between army troops and a rival force. The source of firing was unclear, the witness said, adding air strikes were also heard from time to time. The army said it agreed to a three-day truce to enable people to celebrate the Muslim holiday of Eid al-Fitr. Its adversary, the paramilitary Rapid Support Forces (RSF), said earlier in the day it had agreed to a 72-hour ceasefire, also to mark Eid.…