Yoadimnadji said Chad's government proposed sending troops to help its southern neighbour under a defence pact.
Ethnic violence
He said: "A popular saying goes that if your neighbour's house is on fire, you go to help him, or you risk the fire spreading to your house."
The prime minister added Chad had also suffered repeated incursions by "Sudanese soldiers" over its eastern border, triggering ethnic violence in Chadian communities which had killed more than 300 people in recent weeks.
At the start of the month, Idriss Deby Itno, the Chadian president and Francois Bozize, the president of CAR, accused Sudan of supporting the rebel movements fighting against them.
The Chadian head of state is one of the main supporters of General Bozize, who he helped take power in March 2003 by toppling former president Ange-Felix Patasse.
Sudan's government has repeatedly denied that it is backing rebels in Chad and Central African Republic.