Canada is “extremely disappointed” that China continues to detain two of its citizens, Defense Minister Harjit Sajjan said, as tensions escalate over a case that has roiled ties between the nations for months.

Canada was respecting the rule of law when it arrested Huawei Technologies Co. Chief Financial Officer Meng Wanzhou in Vancouver last December on an American extradition request, Sajjan said in an interview on Saturday. Meng has denied wrongdoing and has continued to fight the extradition in Canadian courts.

“In our democracy, the political system does not interfere with the judicial system and that’s where this process is,” Sajjan said in Singapore, where he’s attending a regional security forum. “We’re extremely disappointed with China’s reaction, having two Canadians arbitrarily detained in this regard. And we seek their immediate release.”

China has repeatedly defended the arrest of Michael Kovrig, who works for the International Crisis Group, and entrepreneur Michael Spavor. Kovrig was arrested on suspicion of spying on state secrets for foreign entities and other intelligence crimes, while Spavor was held on suspicion of stealing state secrets for foreign entities.

Canada has insisted on their release, and Vice President Mike Pence voiced support for the detained Canadians at an appearance Friday with Prime Minister Justin Trudeau. Held in isolation, the two Canadians were questioned multiple times a day and unable to turn off the lights in their cells, Bloomberg reported in December.

“For us, this is extremely black and white,” Sajjan said. “When you sign a treaty, and things happen, you do not politically interfere in the judicial system — it undermines our democracy.”

China has accused Canada of violating a bilateral agreement in arresting Meng, and called for her release.

“I would just remind Canada to realize the consequences of being the cat’s paw for the U.S.,” Geng Shuang, a spokesman for China’s foreign ministry, told reporters in Beijing on Friday. “We hope it will correct its wrongdoing by taking prompt actions to avoid further harm.”