China is “gravely concerned” about the reported killing of two kidnapped Chinese citizens in Pakistan’s southwestern Baluchistan province late last month, the state-run news agency Xinhua said on Friday.

Islamic State killed two Chinese teachers in the province last month, the militant group’s Amaq news agency said on Thursday. A Baluchistan government spokesman had said officials were trying to confirm if the report was true.

“We have taken note of relevant reports and we express our grave concern. We have been trying to rescue the two kidnapped hostages over the past days,” Xinhua quoted Chinese foreign ministry spokeswoman Hua Chunying as saying.

“The Chinese side is working to learn about and verify relevant information through various channels, including working with Pakistani authorities,” Xinhua quoted her as saying. “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.”

Islamic State kills two Chinese teachers kidnapped in Pakistan, agency says

There was no immediate comment from Pakistan’s interior ministry or its foreign office.

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 US$57 billion for its “Belt and Road” trade plan.

“Islamic State fighters killed two Chinese people they had been holding in Baluchistan province, southwest Pakistan,” Amaq said.

Islamic State, which controls some territory in neighbouring 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.

Pakistan’s military published earlier on Thursday 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 Chinese has skyrocketed since 2014 when President Xi Jinping signed off on the China-Pakistan Economic Corridor, pledging to invest US$57 billion in Pakistani road, rail and power infrastructure.

Two Chinese kidnapped in Pakistan in sign of Silk Road perils

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.