Sudan denied yesterday accusations by Chad that it supported gunmen who battled Chadian troops in fighting that killed dozens, the latest tensions between the two nations. Chad's government claimed a day earlier that armed men "backed by the Khartoum government" crossed into Chad on Thursday and attacked the town of Modeina. Twelve Chadian troops and dozens of the attackers were killed, and some 4,000 civilians were driven from their homes, Chad said.Sudanese Army spokesman Brig. Osman Mohamed Al-Aghbash said the accusations of Sudanese support for the fighters were "unfounded and lack substantiating evidence." Khartoum is fully committed to promises made last month in the Libyan capital Tripoli that Sudan and Chad would avoid backing rebels in each other's territory, Al-Aghbash told the official Sudan news agency. "What is happening inside Chad is an internal Chadian question and the Sudanese army has nothing to do with it," he said.