Chad has accused the CAR army of attacking a military outpost on Chad's side of the border, before killing a number of soldiers.
Central African Republic (CAR) soldiers attacked a Chadian military post, killing one soldier, and kidnapping and executing five others, Chad's Defense Ministry said on Sunday.
Chad said the incident amounted to a war crime that "cannot go unpunished."
What are Chad's allegations?
The CAR armed forces attacked the Sourou outpost near the village of Mbere early on Sunday morning, Chad's Foreign Minister Cherif Mahamat Zene said in a statement.
The outpost was manned by 12 soldiers. According to Zene: "They killed a Chadian soldier, injured five and kidnapped five others who were then executed in Mbang on the Central African Republic side."
The base lies near Chad's 1,000-kilometer (approximately 620-mile) border with CAR.
Chad's embassy in the CAR capital of Bangui was told by the head of CAR's military police to collect the bodies of the five executed soldiers, the foreign minister said.
Why was the outpost attacked?
Central African soldiers were pursuing rebels from one of the many armed groups operating in the country across the border, a senior Chadian security official told news agency AFP, speaking on condition of anonymity.
The rebels were members of Unity for Peace in Central Africa (UPC), one of CAR's most powerful armed groups. The UPC is part of a coalition seeking to topple the regime of the country's President Faustin Archange Touadera, the official said.
Chad urges international community to 'bear witness'
Zene said Chad would "call the international community to bear witness" to the incident, notably the UN's 12,000-strong peacekeeping force in CAR, MINUSCA, as well as the African Union and the Economic Community of Central African States (ECCAS).
The Central African Republic regularly accuses its northern neighbor of supporting armed rebel groups from inside Chad.
Chad is in the Sahel region where there are numerous insurgent groups active across porous borders.