Afghan soldiers watch a Soviet army convoy leave Kabul Friday. The Soviet Union informed the United States it intends to pull as many as one-fourth of its troops out of Afghanistan by the end of May, administration and diplomatic sources said Thursday. The accelerated withdrawal would be in keeping with the U.S. insistence that the Soviet troop withdrawal be "front-end loaded" _ meaning more troops would leave in the beginning of the pullout. The official start of the nine-month Soviet military pullout officially begins May 15. Half of the withdrawal is to take place in the first 90 days. There are an estimated 115,000 to 120,000 Soviet troops in Afghanistan.