Rival Burundian factions said Tuesday that peace talks announced for January 6 would not go ahead on time, with no fixed date given for when they might take place.
The small East African country descended into bloodshed in April when President Pierre Nkurunziza announced his intention to run for a controversial third term in a July election that he went on to win.
After talks in Uganda last month, it was announced that talks would resume on January 6 in the Tanzanian town of Arusha.
But the Burundi government delegation said then that "no consensus" had been reached on the date, and presidential press chief Willy Nyamitwe confirmed Tuesday the government delegation would not attend the scheduled talks.
The opposition CNARED coalition also said it would not attend, with spokesman Pancrace Cimpaye saying delegates had "not yet received an invitation" nor been given any date for when the talks might go ahead.
CNARED presents itself as upholding the Arusha peace agreement that ended more than a decade of civil war in 2006, and which it says Nkurunziza has undermined.
There was no immediate response from Uganda, which has been mediating the talks and which had set the January 6 date.