KABUL, Afghanistan—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 …