The government of Chad has insisted the situation in capitol N'Djamena is stable after gunshots were heard near the presidential palace.
Foreign Minister Abderaman Koulamallah said in a video apparently recorded within the palace complex that there had been a "little incident" but that "everything is calm".
Sources close to the African state's government said clashes had occurred between security forces and "terrorist elements".
The French news agency AFP quoted Koulamallah as saying that 18 attackers and a member of the security forces had been killed.
Chad is a landlocked country in northern-central Africa which, since gaining independence from France in 1960, has seen frequent periods of instability and fighting, most recently between government forces and those of Islamist group Boko Haram.
It is led by President Mahamat Déby, who was installed by the military in 2021 after his father, Idriss Déby, was killed in a battle with rebel forces after 30 years in power.
Following the incident on Wednesday, tanks were seen in the area and all roads leading to the palace were closed, the AFP said.
In the video, posted to Facebook, Koulamallah is seen surrounded by members of the government forces.
"Nothing serious has happened," he says.
"We are here and we will defend our country at the price of our blood. Be calm.
"This whole attempt at destabilisation has been thwarted."
He is then seen taking photos and raising his fist with the soldiers.
Koulamallah was quoted by AFP as saying the assault had been launched by a 24-man commando unit, adding that six of the attackers had suffered injuries.
A further three members of the government forces also suffered injuries, he added.
The incident came just hours after a visit to the former French territory by China's Foreign Minister, Wang Yi, who met Déby and other senior officials.
