The gathering of regional heads of state in Tanzania, was meant to focus on the ongoing political crisis in Burundi, after several rounds of mediation failed due to government refusing to meet with exiled opposition groups.
Burundi's absence forced the postponement of the summit to December 27.
Burundi has been locked in crisis since President Pierre Nkurunziza in April 2015 announced he would seek a controversial third term in office, sparking civil unrest that has left 1,200 dead and over 400,000 displaced.
In October 2016 Burundi suspended co-operation with the UN's human rights office over its "complicity" in a report accusing Bujumbura of systematic abuses and warning of a risk of genocide.
In September this year Burundi threatened to quit the rights council altogether after another report pointed to crimes against humanity in the country.
In 2017 Burundi became the first nation to leave the International Criminal Court after it launched a probe into the alleged atrocities in the country.