Peace talks between Afghan officials and the Taliban fell through on Friday in another setback for a resolution to the 18-year-long war.
The meeting known as the intra-Afghan dialogue was set to take place in Qatar this weekend but was cancelled at the last minute because of the high number of delegates that Kabul sought to attend.
The collapse comes at a critical time and amid continued bloodshed. The Taliban now control or influence about half of Afghanistan and 3,804 civilians were killed there last year, according to a UN tally.
Washington, which is leading an effort to end the war, signalled its disappointment and urged both sides to return to the table, though organisers gave no hint about when the conference might be rescheduled.
Sultan Barakat, who heads the group that was to host the event, said in a statement the postponement was "necessary to build further consensus as to who should participate".
"Clearly the moment is not yet right," added Mr Barakat, the director of the Center for Conflict and Humanitarian Studies.
President Ashraf Ghani's administration had on Tuesday announced a list of 250 people from all walks of Afghan life, including government figures, who it wanted to send to Doha.
But the Taliban poured scorn on the lengthy list, saying the conference is "not an invitation to some wedding or other party at a hotel in Kabul".
Though the insurgents insisted they would only talk to Mr Ghani's government in a "personal capacity", any contact between the two parties in Doha would have been hugely significant, especially at a time when Afghanistan is being ripped by fresh violence after the Taliban announced their annual spring offensive.
Kabul blamed the Qatari government for the summit's derailment. In a statement, the presidential palace said Qatar had rejected the long list of delegates and suggested a shorter one which was "not acceptable".
On the Taliban side, the militants complained on Friday that it was "not fair" that Mr Ghani had wanted to send such a large delegation, and that "negotiations with the powerless Kabul administration is a waste of time."
Even some of those Mr Ghani said would attend dropped out, slamming the guest list as rigged to politically strengthen the president, who faces delayed elections in September.
The Doha summit was separate from ongoing direct talks between the Taliban and the US.
While the insurgents did meet with Afghan politicians outside the government in Moscow in February, they have steadfastly refused to meet with Mr Ghani and his administration, which they view as a puppet regime.
US Special Representative to Afghanistan Zalmay Khalilzad said he was "disappointed" the summit had been postponed.
"We're in touch with all parties and encouraged that everyone remains committed to dialogue," the envoy wrote on Twitter.
"I urge all sides to seize the moment and put things back on track by agreeing to a participant list that speaks for all Afghans."
Mr Barakat said both parties had undertaken "tireless and well-intentioned" efforts to find a way for the summit to proceed, but ultimately a "shared understanding on how to achieve inclusivity couldn't be reached."
After US-Taliban talks in February, Mr Khalilzad announced a "draft framework" for a peace deal, though he warned major hurdles remain.