The Organisation of the Islamic Conference has urged Sudan and Chad to exercise self-restraint to defuse growing tension between the neighbours.
Chad says Friday's attack was launched from Sudanese territory
OIC Secretary General Ekmeleddin Ihsanoglu said both sides should use common sense and mature reflection to resolve their conflict.
On Friday, Chad said it was in a "state of war" with Sudan after 100 died in an attack on the border town of Adre.
Khartoum has denied any involvement in the attack.
A statement by the OIC said Mr Ihsanoglu was concerned about the unexpected disturbances, which it said were accompanied by a serious threat of armed conflict.
He "appeals to both countries, both being member states of the Organisation of the Islamic Conference, to resort to common sense and mature reflection to resolve this passing conflict through peaceful and brotherly ways by way of positive dialogue and negotiation," it said.
The statement welcomed the African Union's mediation initiative. The AU said on Saturday that it had sent delegations to the two countries.
Chad says that Sudan is backing rebel groups which have recently sprung up in the east of the country and which are blamed for the attack on Adre, which borders Sudan's troubled Darfur region.
It also accuses Sudanese militia of making daily incursions into Chad, stealing cattle, killing innocent people and burning villages on the Chadian border.
Friday's statement asked Chadians to form a patriotic front against what it called "the common enemy of the nation".
Sudanese officials say Khartoum has never supported Chadian rebel groups.
They accuse N'djamena of deploying planes and troops on Sudanese territory.