Pakistani soldiers stand guard beside a damaged police van at the attack site in southern Pakistani port city of Karachi, on July 21, 2017. At least four people including three policemen were killed and another was injured on Friday evening when unknown gunmen opened fire at a police vehicle in Pakistan's southern port city of Karachi, police said. (Xinhua/Masroor)

ISLAMABAD, July 21 (Xinhua) -- At least four people including three policemen were killed and another was injured on Friday evening when unknown gunmen opened fire at a police vehicle in Pakistan's southern port city of Karachi, police said.

Raja Umar Khattab, a senior police official of the counter-terrorism department, said the incident took place when a group of six gunmen riding on three motorcycles sprayed bullets at a police vehicle in Korangi area of the city.

A police officer, his two constables, and a 12-year-old passerby were killed on the spot, while another passerby was wounded.

Police, security forces and rescue teams rushed to the site and shifted the bodies and injured to the Jinnah Hospital of the city.

The police mobile was on its routine surveillance mission when it came under attack, the officer said.

Seemi Jamali, a spokesperson for the hospital, said that all four victims received multiple bullet wounds, especially at their head and chest.

Pakistan's Federal Interior Minister Chaudhry Nisar Ali Khan condemned the attack and asked the authorities concerned to complete a quick inquiry into the matter and arrest the culprits.

Police and security forces have cordoned off the area and launched a search operation in the nearby residential area.

No group has claimed the attack yet.