All of those who died were from Tanzania. Three others were hurt.
“Hostile” missile fire “fell near the camp where they were staying,” said the Southern African Development Community (Sadc) on Monday.
None of the soldiers has been named, nor have further details been given on where or when the attack took place.
Sadc has also not said who was responsible for the attack on its soldiers.
The southern African regional force was invited in by the Congolese government last year to halt worsening insecurity linked to numerous rebel groups vying for control of territory and eastern DR Congo’s rich mineral resources.
Chief among them is the M23 rebel group, which Rwanda has been widely accused of backing, including by UN experts, although Kigali has always vehemently denied this. In turn, it accuses the Congolese army of working with the FDLR, a militia linked to some of those responsible for the 1994 genocide in Rwanda, a charge rejected by Kinshasa.
After a lull in activity, the notorious M23 rebel group once again saw a resurgence in 2021 and now controls large parts of North Kivu province.
In recent months, thousands of people have fled the escalating violence in parts of eastern DR Congo. Many have taken shelter in the region’s main city of Goma, which some fear the M23 could capture, as it did in 2012.
Pressure has grown on the DR Congo government after it ordered the large UN peacekeeping mission to leave the country by the end of 2024.
A total of 2,900 Sadc soldiers were sent to North Kivu province in December to take on the M23 rebels.
In its statement on Monday, Sadc said a soldier from South Africa had also died in hospital while being treated for health problems.
In February, two South African soldiers were killed by a mortar barrage in North Kivu province.