In a joint statement released Tuesday, Chad and the Central African Republic (CAR) called on the United Nations and the African Union to examine an incident at a border station in which at least six Chadian soldiers were murdered by Central African troops.

Since Chad engaged in African efforts to stabilize CAR in 2013, which has been rocked by rebel insurgencies ever since, the episode threatens to increase tensions between the two nations.

“The two parties recognize the gravity of the situation and emphasize the importance of clarifying the circumstances behind this incident,” the foreign ministers of the two countries said in a joint statement.

Chad’s Defense Ministry on Sunday said that Central African troops had attacked a Chadian military post, killed one soldier, and kidnapped and executed five others – actions it said amounted to a war crime.

CAR authorities said a firefight had broken out by mistake as their soldiers pursued a rebel group near the Chadian border, resulting in the deaths of troops on both sides. They did not specify how many Central African soldiers had died.

A spokesman for Chad’s army told Reuters on Tuesday that more troops had been deployed to the border in response to the incident.

“We were attacked on our territory by the army of a neighboring country. So that this kind of thing does not repeat itself, we are obliged to reinforce security at the border,” General Azem Bermandoa Agouna said.

A delegation from the Central African Republic visited Chad on Tuesday and met with Mahamat Idriss Deby, the son of Chad’s late president Idriss Deby and head of its ruling military council.

After the meeting, representatives of the two countries agreed that an international commission of inquiry made up of agents from the U.N., A.U. and other regional bodies should be formed to investigate the incident.

“Anxious to preserve the centuries-old bonds of brotherhood and friendship, woven by geography and history, the two parties are committed to implementing the findings of the report of the international fact-finding commission,” the statement said.