Former Tanzanian president Benjamin Mkapa wrapped up four days of talks with some 30 Burundian representatives who agreed on the basic problems, but not how to resolve them.
He was tasked with ending problems that erupted when President Pierre Nkurunziza ran for a third term in April 2015, sparking unrest which killed hundreds and left 400,000 displaced.
The biggest hitch is Burundi's fierce opposition to the process as long as it includes exiled main opposition group CNARED which it sees as a "terrorist organisation".
"It is urgent to call a summit of heads of state to examine the obstacles to this process," said Mkapa.
Jean Minai, the president of CNARED, told journalists he had hope that the negotiations could lead to change, but not without Nkurunziza at the table.
"It is only the region's heads of state who could get him to the negotiating table," he said.
However the secretary general of the ruling CNDD-FDD Evariste Ndayishimiye reiterated government's refusal to negotiate with those accused of organising an "insurrection" -- the term used for the protests that erupted after Nkurunziza announced his third term bid.
CNARED is also accused of leading a foiled coup plot in May 2015, which they deny.
Mkapa had hoped this week's talks would lead to a statement by all parties denouncing violence, agreeing not to change the Arusha peace accords which ended Burundi's civil war in 2006 or the constitution, and agreeing plans for 2020 polls.
But between the government which claims that there is no crisis in Burundi and wants to focus on the next election, and the opposition demanding a transition administration and the departure of Nkurunziza before 2020, no consensus was reached, a diplomat told AFP on condition of anonymity.
Despite the government boycott, a representative from the ruling CNDD-FDD was present at the talks.
In a sign of Bujumbura's hostility, the Burundi embassy wrote a letter Friday asking Tanzanian officials to arrest the CNARED representatives.
Rights groups and the United Nations have detailed atrocities before and after the election, with some warning of "genocide" in a country with a long history of violence between its Hutu and Tutsi communities.
The government has rejected criticism from the international community, and Nkurunziza has hinted he may run for a fourth term in 2020. Efforts to reform the constitution have raised fears he may remove term limits.
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