Beijing says nine Chinese workers were among 12 people killed in a "bomb attack" on a bus in northwestern Pakistan, though local officials say the explosion appeared to have been caused by a gas leak.
The bus was carrying around 40 Chinese personnel to a hydropower dam construction site in Pakistan's northern Khyber Pakhtunkhwa Province near the border with China.
China is building the Dasu hydropower project (DHP) in the district of Upper Kohistan of Khyber Pakhtunkhwa under an investment plan that is part of Beijing's Belt and Road Initiative.
China is Islamabad's closest regional ally, but the security of Chinese workers in Pakistan has long raised concerns in Beijing.
Officials from both countries said nine Chinese workers and three Pakistani members of the paramilitary police who were ensuring the Chinese workers' security died in the blast.
Arif Khan Yousafzai, a senior government official in the Upper Kohistan district, said around 28 people were also injured and airlifted to hospitals by the Pakistani military.
Chinese Foreign Ministry spokesman Zhao Lijian voiced "shock and condemnation over the bombing" and urged Pakistan to "severely punish" those responsible and "earnestly protect" Chinese nationals and projects.
Local officials acknowledged an explosion occurred aboard the bus, but the Pakistani Foreign Ministry contradicted the Chinese account, saying in a statement that the bus "plunged into a ravine after a mechanical failure, resulting in the leakage of gas that caused a blast."
The DHP, which includes the construction of a 4,320MW hydropower plant on the Indus River near Dasu town, is part of the China-Pakistan Economic Corridor (CPEC), a $65 billion investment plan under Beijing's Belt and Road Initiative that is aimed at connecting western China to the Gwadar deep-water sea port in southern Pakistan.
Access to Gwadar will give China strategic access to the Arabian Sea.
Construction of the dam began in 2017 and was scheduled to be built within five years, according to the Pakistan Water and Power Development Authority.
China has invested billions of dollars into Pakistan in recent years, but Chinese-funded projects have triggered the discontent of separatist groups in Pakistan's Balochistan, who say local communities have little benefit.
In April, the Pakistani Taliban claimed responsibility for a deadly suicide explosion at a luxury hotel hosting the Chinese ambassador in southwest Balochistan. The ambassador escaped unhurt.
In 2019, gunmen stormed a luxury hotel in Balochistan overlooking the construction of the Gwadar port, killing at least eight people.