Ekmeleddin Ihsanoglu, the secretary-general of the world's largest Islamic body, said on Sunday that the two countries should "demonstrate self-restraint and calm the situation", after Chad's accusation that Sudan was trying to destabilise its government.
He appealed to the two members of OIC to "resort to common sense and mature reflection to resolve this passing conflict through peaceful and brotherly way".
The African Union said on Saturday that it had sent a delegation to Chad and Sudan to try to ease tensions as Chad declared that it was in a "state of belligerence" with Sudan.
Chad alleges that Khartoum is hosting rebels and a growing number of Chadian army deserters in western Sudan, from where an attack was mounted on Chad's eastern frontier town of Adre last Sunday.
Several new rebel groups have sprung up recently in eastern Chad, a region inundated by some 200,000 refugees from the civil war in Sudan's Darfur region.
Khartoum had accused Ndjamena of deploying aircraft and troops on its territory before the latest incident.