China has accused two Canadians of spying, as tensions between the nations grow over the possible extradition of a Huawei executive to the US.
Michael Kovrig, a former diplomat, and Michael Spavor, a businessman, were detained in December after Meng Wanzhou was arrested in Canada on suspicion of fraud and breaching sanctions on Iran.
Ms Meng is suing Canada over her arrest, which was made at the request of the US.
China has condemned Ms Meng's arrest.
The diplomatic spat has hurt Canada-China relations, and the arrest of the two Canadians had been seen as Beijing's retaliation for its detention of Ms Meng, reports the BBC.
Canada officially launched her extradition process on Friday but the legal process can be lengthy and remains in its early stages.
Speaking to journalists on Monday, Prime Minister Justin Trudeau said his government was "very concerned with this position that China has taken" on the two detained men.
"It is unfortunate that China continues to move forward on these arbitrary detentions, and we will continue to stand up for these Canadians," he said.
Mr Trudeau has previously called for the release of both men.
