At least four people were killed in Chad's capital, N'Djamena, as government forces foiled a "destabilisation plot" against President Idriss Deby, officials said.
Two army generals, a ruling coalition MP and an opposition MP had been arrested over the alleged plot, the officials added.
A "small group" conspired for four months, the officials said.
Chad, a staunch ally of France, has a long history of coups and revolts.
Mr Deby himself seized power in a coup in 1990.
The BBC's Nathalie Magnien in N'Djamena says it is business as usual in the capital and no-one seems particularly concerned about the news.
There is no visible sign of increased security in the city or patrols on the streets, she says.
"Between four and eight people were killed in fighting at a military barracks in the east of N'Djamena," said a police source who requested anonymity, Reuters news agency reports.
Police sources told the AFP news agency a shoot-out took place on the outskirts of N'Djamena, with three members of the security forces being among the dead.
"A small group of ill-intentioned individuals attempted to carry out a destabilisation plot against the institutions of the republic," a government statement said.
It said that the country's security forces "neutralised" them, without specifying how many people were involved in the alleged action.
Prosecutor Mahamat Saleh Youssouf named the generals who had been arrested as Weiddig Assi Assoue and Ngomine Beadmadji David.
Ruling coalition MP Mahamat Malloum and opposition MP Saleh Makki had also been arrested, he said.
Mr Makki's coalition Co-ordination of Political Parties for the Defence of the Constitution (CPDC), told the BBC it was confused by his arrest.
Mr Makki was arrested by police between 21:00 and 22:00 local time on Wednesday evening, his wife told the CPDC.
Our reporter says it is not clear what charges they will face.
Since its independence from France in 1960, Chad's history has been marked by instability and violence stemming mostly from tension between the mainly Arab-Muslim north and the predominantly Christian and animist south.
Mr Deby has survived two attacks on the capital - in 2006 and 2008 - from rebels in eastern Chad.
These rebels were supported by Sudan's government, which was unhappy that Darfuri rebels were using eastern Chad as a base. But a rapprochement between Chad and Sudan in 2010 has helped bring peace to that region.
Earlier this year, Chad deployed some 2,000 troops to help French forces oust Islamists who had seized large swathes of territory in Mali.
France said it had noted the latest events in Chad "with concern" and called on the government and opposition to engage in "calm and constructive dialogue", AFP reports.