Islamic State has killed two Chinese teachers it kidnapped in Pakistan's southwestern Baluchistan province last month, the militant group's Amaq news agency said on Thursday, in a blow to Islamabad's efforts to safeguard Chinese workers, Reuters reported.
China's Foreign Ministry said it was "gravely concerned" about the report and working to verify the information.
Armed men pretending to be policemen kidnapped the two language teachers in the provincial capital, Quetta, on May 24. The kidnapping was a rare security incident involving Chinese nationals in Pakistan, where Beijing has pledged $57 billion for its "Belt and Road" plan.
"Islamic State fighters killed two Chinese people they had been holding in Baluchistan province, southwest Pakistan," Amaq said.
A Baluchistan government spokesman said officials were in the process of confirming "whether the report is true".
China's Foreign Ministry said it noted the report and expressed "grave concern".
"We have been trying to rescue the two kidnapped hostages over the past days," the ministry said in a short statement.
"The Chinese side is working to learn about and verify relevant information through various channels, including working with Pakistani authorities," it said.
"The Chinese side is firmly opposed to the acts of kidnapping civilians in any form, as well as terrorism and extreme violence in any form."
There was no immediate comment from Pakistan's interior ministry or its foreign office.
Islamic State, which controls some territory in neighboring Afghanistan, has struggled to establish a presence in Pakistan. But it has claimed several major attacks, including one on the deputy chairman of the Senate last month in Baluchistan, in which 25 people were killed.
Earlier on Thursday, Pakistan's military published details of a three-day raid on a militant hideout in a cave not far from Quetta, saying it had killed 12 "hardcore terrorists" from a banned local Islamist group and prevented Islamic State from gaining a "foothold" in Baluchistan.
China's ambassador to Pakistan and other officials have often urged Islamabad to improve security, especially in Baluchistan, where China is building a new port and funding roads to link its western regions with the Arabian Sea.
The numbers of Pakistanis studying Mandarin has skyrocketed since 2014, when President Xi Jinping signed off on the China-Pakistan Economic Corridor, pledging to invest $57 billion in Pakistani road, rail and power infrastructure.
Security in Baluchistan has improved in recent years.
However, separatists, who view the project as a ruse to steal natural resources, killed 10 Pakistani workers building a road near the new port of Gwadar this month, a key part of the economic corridor.
China has also expressed concern about militants in Pakistan linking up with what China views as separatists in the far western Chinese region of Xinjiang, where hundreds have been killed in violence in recent years.