By Yew Lun Tian
BEIJING -Chinese Premier Li Keqiang has urged his Pakistani counterpart to hold accountable the culprits in what he described as a "terrorist attack" on a bus ferrying Chinese workers, state media said on Friday.
Li, the most senior Chinese politician to have spoken on the incident so far, spoke with Pakistani Prime Minister Imran Khan by phone on Friday, according to Xinhua news agency.
An explosion on a bus in northern Pakistan on Wednesday sent it hurtling over a ravine and killed 13 people, including nine Chinese nationals.
Li has asked Pakistan to "use all necessary measures" to investigate the incident and hold the culprits accountable, according to Xinhua.
China is a close ally and major investor in Pakistan, and various militants opposed to the Pakistani government have in the past attacked Chinese projects.
The Chinese workers killed on the bus were employed at the Dasu hydroelectric project, part of the China-Pakistan Economic Corridor (CPEC), a $65 billion investment plan aiming to link western China to the southern Pakistani port of Gwadar.
CPEC is part of Beijing's massive Belt and Road Initiative.
Pakistan originally blamed a mechanical failure for the blast but on Thursday Information Minister Fawad Chaudhry said traces of explosives were detected and that "a terrorist attack cannot be ruled out" as the cause of the incident.
China, which initially called it a "bomb attack", was more circumspect on Thursday, referring to it as an "incident" before describing it as a "terrorist attack" on Friday as a joint investigation of the incident carries on.