NEW : 42 killed in Afghanistan market attack . NEW : The Abdulrahimzai says it 's the single worst attack Tuesday in Paktika . The device was detonated by a suicide bomber , a police official says . Security remains a major concern in Afghanistan , from which the United States is due to withdraw most of its troops by year 's end . Afghanistan continues to face major security challenges .
NEW : 42 killed in Afghanistan market attack . NEW : The Abdulrahimzai says it 's the single worst attack Tuesday in Paktika . The device was detonated by a suicide bomber , a police official says . Afghanistan continues to face major security challenges .