Canadian businessman Michael Spavor, who worked with North Korea, is being investigated on suspicion of harming China’s state security, officials said, days after a former Canadian diplomat was detained in China in an escalating diplomatic row.

The state security bureau in the northeastern Chinese city of Dandong, which borders North Korea, has been investigating Spavor since Dec. 10, an official news site for the Liaoning province government said on Thursday, according to Reuters.

It did not give further details.

The announcement follows the detention in Beijing on Monday of former diplomat Michael Kovrig, who works for the International Crisis Group (ICG). State media in China has reported Kovrig is being investigated on the same charges.

China has reacted angrily to Canada’s arrest on Dec. 1 of Chinese executive Meng Wanzhou, the chief financial officer of China’s Huawei Technologies, and Spavor’s investigation is likely to further escalate the diplomatic row.

Meng’s arrest was made at Washington’s request. She has been accused by US prosecutors of misleading banks about transactions linked to Iran, putting the banks at risk of violating sanctions.

Officials say China had so far not tied Kovrig’s detention to Meng’s arrest, although Canadian diplomatic experts have said they have no doubt the two cases are linked.

Canada has been unable to contact Spavor since he notified the government that he was being questioned by Chinese authorities, Foreign Ministry spokesman Guillaume Bérubé said in a statement issued in Canada late on Wednesday.

Canadian officials were working hard to ascertain Spavor’s whereabouts and would continue to raise the issue with the Chinese government, Bérubé said.

Phone calls, messages and emails to Spavor went unanswered on Thursday.

Friends of Spavor said he was due to fly out of Dalian, in Liaoning province, on a Korean Air flight to South Korea at 2:05 p.m. (0605 GMT) on Monday but had not arrived.

Kovrig and Spavor were acquainted, according to people who know them, although there has been no official indication from the Chinese government that their cases are linked or are related to North Korea.

Kovrig had carried out research on China’s diplomatic ties to North Korea in his work on Chinese security issues for the ICG, a think tank focusing on conflict resolution.

Spavor, who is based in Dandong, is the head of Paektu Cultural Exchange, a China- and UK-based non-profit social enterprise.

The group says on its website it is “dedicated to facilitating sustainable cooperation, cross-cultural exchanges, activities, trade, and investment” with North Korea.

It also says the organization maintains an “array of contacts” within North Korea and is “non-political”.

Spavor has acted as a translator and facilitator for former US National Basketball Association star Dennis Rodman on trips to North Korea and shared Long Island Iced Teas with North Korean leader Kim Jong Un on board one of his private boats after they went jet-skiing in 2013.

More recently, he has been trying to facilitate investment in North Korea in anticipation of sanctions being lifted, often hosting both North Korean officials and potential investors at his office in Dandong, as well as on trips inside North Korea, Spavor had said previously.

China’s foreign ministry suggested on Wednesday that Kovrig might have broken China’s laws on the management of non-governmental organizations (NGOs) if he was conducting work in China for the ICG, which is not registered.