People gather at the explosion site after an attack killing around 16 people and wounding 53 others in Sadr City in eastern Baghdad, Iraq, on May 17, 2016. (Xinhua/Khalil Dawood)

Security forces arrive at the explosion site after an attack killing around 16 people and wounding 53 others in Sadr City in eastern Baghdad, Iraq, on May 17, 2016. (Xinhua/Khalil Dawood)

People gather at the explosion site after an attack killing around 16 people and wounding 53 others in Sadr City in eastern Baghdad, Iraq, on May 17, 2016. (Xinhua/Khalil Dawood)