Gunshots and explosions have been passed by rebel leaders in recent rallies in cities occupied by the Democratic Republic of the Congo.
The video shows a chaotic scene, with bodies on the street fleeing the rally in Bukavu, the second largest city in panicked.
The number of casualties is not clear, but AFP quoted hospital sources as saying at least 11 people were killed and another 60 were injured.
This is the first rally held by Rwanda-backed rebels in Bukav, taking cities from government forces after rapid progress from the region earlier this month.
Rebels accused President Felix Tshisekedi's administration of orchestrating the attack.
However, Tshisekedi blamed it on the “foreign military” he said operated in the East.
The rally was earlier delivered by Corneille Nangaa, head of the coalition of rebel groups including Rwanda-backed M23.
He assured the crowd that the rebels would bring safety and security to the city.
“Special units and patrols will take place in all communes,” Reuters reported.
Nangaa and Bertrand Bisimwa of M23 are believed to have left when the main square of Bukavu happened.
Two people were arrested for the attack and were looking for other suspects, Nanca said in a statement.
“This kind of timid and savage behavior will not have no consequences,” he said.
Rebels have been advancing in the Congo Doctor since January, capturing Bukavu and Goma, the largest cities in the region.
The fight forced about 500,000 people to leave their homes, worsening the already serious humanitarian crisis, the United Nations said.
The African Union and the United Nations have called for a ceasefire and demanded that the rebels withdraw from the areas they now control.
Rwanda once denied support for the M23, but recently it has adopted a more defensive approach, saying the battle near the border between the Congo Doctor and Rwanda is a threat to its security.
UN experts previously estimated that between 3,000 and 4,000 Rwandan troops were present in the east of Dr. Congo.
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