China says it is holding a Canadian man on suspicion of stealing state secrets but has released his wife on bail.
Kevin and Julia Garratt, a Christian couple, run a coffee shop in Dandong on the North Korean border.
They were seized by investigators six months ago. State media said then that they were suspected of stealing secrets about defence and the military.
Canada says it is "very concerned" about the case and will continue to pursue it.
"While we welcome the recent decision to release Julia Garratt, the government of Canada remains very concerned with the detention of Mr Garratt," Reuters quoted a statement from office of Junior Foreign Minister Lynne Yelich as saying.
"We have raised the case at the highest levels and will continue to raise it with senior officials."
At a press conference on Thursday, Chinese foreign ministry spokesman Hong Lei said Kevin Garratt had been placed in criminal detention "on the charge of spying and stealing state secrets".
Julia Garratt had been granted bail pending trial, he said.
"The relevant case is under investigation. The Chinese government will protect their lawful rights and interests in accordance with law," Mr Hong added.
The Chinese and North Korean flags attached to a railing as trucks carrying Chinese-made goods cross into North Korea on the Sino-Korean Friendship Bridge at the Chinese border town of Dandong on 18 December 2013
The couple live in Dandong, at the main China-North Korea border
In a statement, a lawyer for the family said that the couple had not been formally arrested or charged, and "no evidence of any crime" had been presented.
"We call upon the Chinese government to ensure that this matter is handled with transparency and due process as required by Chinese law and fundamental international standards," lawyer James Zimmerman said in a statement.
When the couple were arrested their son, Simeon, said the move made "absolutely no sense".
The couple taught in southern China for several years and then moved to Dandong, where they opened Peter's Coffee House.
Dandong is the main China-North Korea border crossing and trade link. It is a key transit point for North Korean refugees, some of whom are aided by NGOs or Christian groups.
Correspondents describe China's "state secrets" law as notoriously vague, including the definition of what constitutes a state secret.
The detention of the couple came shortly after Canada announced that a top government research organisation had been struck by Chinese "state-sponsored" hackers.
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