Turkey announced the suspension of talks between Afghanistan's warring sides until after Ramadan and Eid Al Fitr – hours after a suicide bombing in Kabul injured four people.
The suicide bomber struck as an Afghan security convoy was travelling in the capital.
Afghanistan's interior ministry said civilians and security personnel were among the wounded.
No group claimed responsibility.
The attack was the first in weeks in the capital, even as targeted killings escalated and Afghanistan's security personnel came under relentless attacks by Taliban insurgents.
Residents fear the attack could be a harbinger of what is to come as the US and Nato prepare to begin their withdrawal from Afghanistan expected to be completed by September 11, the 20th anniversary of the deadly terrorist attacks in America.
The attacks carried out by Al Qaeda were plotted in Afghanistan while the country was ruled by the hardline religious militia.
It had been hoped Afghanistan’s rival sides would reach a peace pact at the talks in Turkey, to end decades of war.
US State Department spokesman Ned Price did not confirm the postponement but said broader diplomatic efforts will continue: "We've always been clear, Istanbul was not a replacement for Doha."
Taliban and Afghan government negotiators began peace talks last year in the Qatari capital of Doha, but progress was slow and violence continued to escalate in Afghanistan.
Washington was trying to speed up the process, which included pushing for the summit in Turkey that was to be attended by more than 20 countries and global bodies.
UN spokesman Stephane Dujarric said on Tuesday that he could not confirm if the conference had been postponed.
"The United Nations, along with the co-conveners, Qatar, Turkey, we're continuing to engage with representatives of both the Islamic Republic of Afghanistan and the Taliban on ways to strengthen and add impetus to the intra-Afghan negotiations," Mr Dujarric said.
The UN special envoy for Afghanistan, Deborah Lyons, was in Doha last week to discuss with Afghan parties "the best way the international community can support them in making progress on their negotiations towards a just and durable political settlement", Mr Dujarric said.
"Our focus will continue to be on progress in intra-Afghan negotiations, which is a critical part of the way forward."
A leading US general voiced "grave doubts" on Tuesday about the Taliban's reliability as a negotiating partner for Washington and Afghan diplomats in the event of the military's full withdrawal from America's longest war.
The Islamist Taliban ruled Afghanistan from 1996 to 2001, when they were ousted by US-led forces. Since then, they have waged a long-running insurgency and still control wide several areas of the country.