Hourmadji Moussa Doumgor, a government spokesman, told reporters on Friday: "Chad is today in a state of belligerence with Sudan. The friends of Chad must support it by all means possible in this ordeal."
The comments came a day after Idriss Deby, the president of Chad, accused his Sudanese counterpart of plotting to destabilise his country, blaming Khartoum for a rebel attack on the frontier town of Adre.
The president made the accusation during a visit to the town to decorate troops who killed about 100 rebels while repelling the attack by forces of the Rally for Democracy and Liberty.
Doumgor said: "The government of Chad believes that one must not stop at simple condemnations of principle but that the enemy of Chad must be pointed out ... [Sudanese] president Omar Hassan Ahmed el Bechir."
There has been a flurry of accusations between Ndjamena and Khartoum in recent weeks, with Chad alleging that Sudan has been happy to host its rebels and a growing wave of army deserters in order to destabilise the country.
Sudan has said that Chad had already deployed aircraft and troops on its territory before the latest incident, allegations denied by Ndjamena.
Several new rebel groups have sprung up recently in eastern Chad, which plays host to about 200,000 refugees from the civil war in the Darfur region of Sudan.