Chadian President Idriss Deby told a rally in N'Djamena, the capital, reported the BBC, "We have taken the decision to break our diplomatic relations with Sudan today and to proceed to close our frontiers."
Rebels stormed into N'Djamena on Thursday in an attempt to overthrow the president. The army fought back with tanks and attack helicopters.
The shootout lasted three hours, according to the BBC, and yielded a bloody, glass-strewn mess.
Gen. Mahamet Ali Abdullah said he did not have a breakdown of the 350 people killed during Thursday's assault on N'Djamena, but he said the toll included government troops, rebel forces and civilians, reported the Associated Press.
He said the army captured 271 rebels and 14 pickups they used, some mounted with anti-tank weapons, anti-aircraft guns and missile launchers. Troops paraded the rebel prisoners and laid out the bodies of dead insurgents at the National Assembly building on Friday, reported the AP.
This is the second attempt to overthrow the president in less than a month. Rebels have vowed to usurp Deby -- who seized power in a 1990 coup -- before the elections scheduled for early May.
Deby, who ordered Sudanese diplomats out of the country, has repeatedly portrayed the rebels attempting to overthrow him as mercenaries employed by Sudan, a charge Sudanese officials deny, reported the AP.
But the rebels -- the United Front for Change, a coalition of several armed groups and some Chadian army deserters who helped Deby rise to power -- are based in Darfur, the western portion of Sudan.
For the past six months, the leader Mahamat Nour has been building up his forces in bases in Darfur, the lawless Sudanese region across Chad's eastern border, from where both Deby and before him ex-President Hissene Habre launched their coups, reported the BBC.
Chad declared victory over the rebels Friday, invited the press into the National Assembly building and called upon the international community to solve the conflict in Darfur. Otherwise, Deby said Chad would expel some 200,000 Sudanese refugees to "another country."
"The international community has been totally deaf and dumb on the situation between Sudan and Chad," Deby said following an emergency Cabinet meeting. They "need to understand the situation and that enough is enough."
The U.N. Security Council and the African Union Peace and Security Council both condemned the attack and called on Chad and Sudan to prevent any more violence or an escalation of tensions, reported the AP.
U.S. Deputy Secretary of State Robert Zoellick on Friday called for an end to the violence and blamed a breakdown in the political process in Chad:
"Despite our efforts and that of the French and that of the African Union, there has not been a satisfactory coming together of the Deby regime and some of the opposition for either a fair election or some inclusive political process," Zoellick said at the Brooking Institution in Washington, D.C.
Chad, an arid, landlocked country of 10 million about three times the size of France, has been wracked by violence for most of its history, with more than 30 years of civil war since independence from France in 1960 and different small-scale insurgencies since 1998.