Two Democratic Republic of Congo soldiers were killed in an "incident" with Burundi troops at the Lake Tanganyika border, Congolese sources said Tuesday.
"The incident came about due to a lack of communications, but also because of the darkness of the lake," DR Congo army spokesman Dieudonne Kasereka told AFP.
"The Congolese navy was on a reconnaissance patrol when it when it was mistaken for bandits by the Burundian navy," he added.
Two Congolese were killed and another captured during the fighting which happened on Monday night, he said.
Burundi's government disputed the details of the incident as well as the toll.
In a statement released late Tuesday, Burundi's public security ministry said its soldiers had attacked "a group of four bandits armed with guns" around 2 am, shooting dead two of the men while the other two drowned in the lake.
"The identity of these bandits remains unknown. Investigations are ongoing," the ministry said, adding that its forces had seized weapons from them, including two Kalashnikov rifles.
A local official in Mboko, in eastern DRC, said the two sides exchanged gunfire after the Congolese military "attacked Burundian fishermen from whom they had taken five litres of fuel".
Tanganyika is the second largest lake in Africa, running nearly 680 kilometres (425 miles) north to south.
Its shores are in four countries; DRC, Burundi, Zambia and Tanzania.