In social media, images are circulating where people are fleeing from the meeting in panic and bloody bodies are lying on the ground in the city of Bukavu.
A hospital source tells AFP that at least eleven people have been killed and around 60 people injured.
President Felix Tshisekedi calls the explosions a "heinous terrorist act".
Among the leaders present were, among others, Corneille Nangaa, leader of a coalition of groups including M23. He and others were on their way to leave the scene when two explosions occurred, according to a journalist on the spot.
M23 has swept through the region, taking over key cities and killing thousands of people. In a lightning-fast offensive a few weeks ago, the group took over the largest city in eastern Congo, Goma, and the second-largest city, Bukavu.
M23 has the support of thousands of soldiers from neighboring Rwanda, according to UN experts. The militia claims to have set its sights on the country's capital, Kinshasa, which is hundreds of miles further west.
