KABUL -- Turkey announced early Wednesday that a conference Washington had hoped would move Afghanistan's warring sides to a final peace agreement was postponed, as fresh violence rattled the Afghan capital.

The postponement of the conference, which was to have begun Saturday in Istanbul, underscored the difficulties the Biden administration is facing in orchestrating an orderly exit from conflict-scarred Afghanistan. The U.S. has said it would begin withdrawing its remaining troops from the country on May 1 and complete the pullout by Sept. 11, no matter what.

In a TV interview, Turkish Foreign Minister Mevlut Cavusoglu said the conference was delayed until after the Islamic fasting month of Ramadan, which ends in mid-May.

Just hours before his announcement, a suicide bomber attacked a convoy of Afghan security personnel, wounding five people in Kabul. The interior ministry said civilians and security personnel were among the wounded.

The attack was the first in weeks in the capital, even as targeted killings have escalated and Afghanistan's security personnel have come under relentless attacks by Taliban insurgents. Recent months have also seen an increase in government bombing raids on suspected Taliban positions and increased raids by Afghan special forces.

Residents fear the attack could be a harbinger of what's to come as the U.S. and NATO prepare to begin their final withdrawal from Afghanistan. No one took immediate responsibility for the attack.

Cavusoglu sad the conference, which was expected to begin on Saturday, was postponed because of "lack of clarity" by the participants, without elaborating.

Until now Taliban insurgents have refused to sign on to the conference even as Pakistan, where their leadership council resides, has been pressing the hardline Islamic militia to attend.

The Taliban have accused Washington of breaching an agreement signed last year under which the U.S. was to have withdrawn the last of its troops by May 1.

But President Joe Biden, who inherited that deal with the Taliban from his predecessor, last week said the remaining estimated 2,500 troops would begin leaving on May 1. All American and NATO soldiers would be gone by Sept. 11, the 20th anniversary of the terrorist assault on the U.S. that launched the U.S.-led invasion to hunt down al Qaida's leader Osama bin Laden.

On Sunday, the Taliban issued an English-language statement on their Al Emara site, indicating they were not ready to attend the conference. They claimed that a powerful propaganda campaign had been launched, hyping expectations that a peace deal would be reached at the end of the planned 10-day meeting.

The statement said this was an attempt "to push the Taliban, willingly or unwillingly, to a rushed decision which was needed by America." It alleged that the aim of the conference was to "complete a for-show road map before the withdrawal of foreign forces."

In Kabul, Afghan government-allied negotiators had anticipated a delay as none had received an invitation to the conference and several were without visas to Turkey.

In Washington the U.S. State Department spokesman Ned Price would not confirm the postponement but said the U.S. would continue diplomatic efforts to reach a peace deal.

"When it comes to the talks in Istanbul, this gets to the point that, from the very earliest days of the Biden administration, we have recognized ... that there is no military solution to the conflict in Afghanistan, and only through a political settlement and a comprehensive ceasefire will we be able to support a resolution that brings a security, stability, and prosperity to the people of Afghanistan," Price said in a statement.

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Associated Press Writers Suzan Fraser in Ankara, Turkey and Matthew Lee in Washington contributed to this story.