A Zimbabwean kidnapped while working for Canadian gold miner Banro in eastern DR Congo was freed on Wednesday after nearly three weeks in captivity, the army said.
A South African captured with the Zimbabwean and two local Congolese last month is still being held as negotiations for his release continue.
The four Banro workers were taken hostage on July 26 when they were ambushed by an armed militia in Salamabila, a mining town in Maniema province in DR Congo's restive east.
On Tuesday, the two local Congolese workers were released by what a local journalist reported was a Mai-Mai militia group that had abducted them.
"Among the four hostages, the two Congolese and now the Zimbabwean... have been released. The South African is still captive in the bush," said Captain Dieudonne Kasereka, an army spokesman for the region.
"A delegation from Kinshasa and Bukavu is in negotiations in Salamabila with the kidnappers to secure the release of the South African expert from Banro in the coming hours."
The Zimbabwean has been named by the foreign ministry in Harare as Nephias Rudovo.
New York and Toronto-listed Banro's two gold mines in the DRC's east have been troubled by illegal miners and armed groups operating there.
Banro operates two gold mines in the east, one in Twangiza in South Kivu province and the other in Namoya in Maniema state.
A Frenchman working for Banro was kidnapped in March 2017 but later freed. The company stopped operations that year at a third mine after a deadly attack.
The Mai-Mai are self-described "self-defence" groups who were armed during the Second Congo War (1998-2003) by authorities in the distant capital Kinshasa to fight off Ugandan and Rwandan forces.
But many of the militiamen kept their weapons after the war, and fighting between the groups and the Congolese army continues both in North and South Kivu.