UN chief Antonio Guterres on Saturday demanded the Democratic Republic of Congo's "territorial integrity" be respected and a regional war avoided, at an African summit the day after Rwandan-backed fighters seized a second DRC provincial capital.
With international pressure mounting on Rwanda to curb the fighting in eastern DR Congo (DRC), the conflict was set to dominate the African Union summit, which opened in the Ethiopian capital Addis Ababa on Saturday morning.
Rwanda's President Paul Kagame was seen attending meetings at the gathering, but Congolese President Felix Tshisekedi was absent from the summit as fighters from the M23 group took more territory.
Having routed the Congolese army to capture the key provincial capital of Goma in North Kivu last month, the Rwandan-backed armed group has since pushed into neighbouring South Kivu.
It took a key airport there before marching largely unchecked into the city of Bukavu on Friday, security and humanitarian sources said.
"The fighting that is raging in South Kivu -- as a result of the continuation of the M23 offensive -- threatens to push the entire region over the precipice," Guterres told leaders in an address to the summit, without mentioning Rwanda.
He urged dialogue, saying that a regional escalation must be avoided "at all costs" and that there was "no military solution".
"And the sovereignty and territorial integrity of the DRC must be respected," he said.
The AU has been criticised for its timid approach in the face of a possible regional conflagration, and observers have demanded more decisive action.
The European Union said on Saturday it was "urgently" considering all options following the news from Bukavu.
"The ongoing violation of the DRC's territorial integrity will not go unanswered," it warned.
However, Guterres stressed in a later press conference that Africa was "the key to the solution of the problem".
East and southern African leaders on February 8 called for an "immediate and unconditional" ceasefire within five days, but fresh fighting erupted on Tuesday.
A meeting of the AU's Peace and Security Council dedicated to the conflict ran late into the evening on Friday, with neither Kagame nor Tshisekedi attending.
A government source told AFP that Tshisekedi would not be at the summit over the weekend either as he had to "closely follow the situation on the ground in DRC".
AFP journalists in Bukavu reported sporadic gunfire on Saturday, with the streets deserted as residents sheltered inside after reports of overnight looting.
Across the nearby border in Rwanda, AFP reporters in the town of Rusizi said the streets were unusually calm but some gunshots could be heard.
Tshisekedi, speaking at the Munich Security Conference on Friday, urged nations to "blacklist" Rwanda, condemning Kigali's "expansionist ambitions".
Rwanda has not admitted backing M23 but has accused extremist Hutu groups in DRC of threatening its security.
DRC accuses Rwanda of plundering valuable minerals in its eastern provinces.
Neighbouring Burundi has also sent thousands of troops to support the struggling Congolese army.
The 55-nation AU is meeting as Africa faces another devastating conflict in Sudan and after US President Donald Trump cut US development aid, hitting the continent hard.
Leaders opened the summit by calling for progress on securing reparations for past abuses by colonial powers -- a growing issue in international talks.
The AU leaders represent around 1.5 billion people in a body that observers have long branded ineffective, most recently over the DRC violence.
"Kagame has clearly calculated that his best approach is to push forward, and he does have some support," International Crisis Group's Great Lakes project director Richard Moncrieff told AFP.
"Some African leaders have trouble defending Congo because they don't defend themselves."
Angolan President Joao Lourenco, involved for several years in futile mediation between Tshisekedi and Kagame, took over the rotating presidency of the AU in Saturday's session -- a ceremonial role that changes hands annually.
In a twist, leaders voted Saturday to elect Dijbouti's Mahmoud Ali Youssouf as the new chairman of the body's executive commission -- the AU's top job -- replacing Chad's Moussa Faki Mahamat at the end of his two-term limit.
"We won, we have secured the most votes, and we won," Djiboutian presidential spokesman Alexis Mohamed said.
Youssouf saw off competition from Kenyan opposition veteran Raila Odinga and Madagascar's ex-foreign minister Richard Randriamandrato.
