Passengers aboard the subway train in Mashhad, Iran, on Feb 21, 2017. [Photo by Tang Mo/Provided to chinadaily.com.cn]

China-made subway trains will start operation in the Iranian city Mashhad in May 2017.

Running on Line 2, a 13-kilometer stretch through the northern part of the city to the southern part, the trains are manufactured by CRRC Changchun Railway Vehicles Co., Ltd.

The line held its operation ceremony on Tuesday.

The CRRC is China's rail manufacturer and exporter.

Cui Zhongxia contributed to the story.