KABUL: A Washington-backed Afghan peace conference in Turkey has been postponed over non-participation by the Taliban, three sources told Reuters.

The meeting was scheduled for April 24 to fast-track an agreement between the Taliban insurgents and the Afghan government in light of the announcement by Washington that foreign troops would leave Afghanistan by Sept. 11.

"The Istanbul meeting is not happening on the given date because the Taliban refused to attend," a senior Afghan government official told Reuters.

The postponement was confirmed by two other sources, including one official whose country is involved in the planning process. There was no immediate revised date.

U.S. 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".

An Afghan government spokesman did not immediately respond to a request for comment.

UN spokesman Stephane Dujarric said earlier 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," Dujarric told reporters.

The U.N. 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 toward a just and durable political settlement," Dujarric said.

"Our focus will continue to be on progress in intra-Afghan negotiations, which is a critical part of the way forward."