OTTAWA (AFP) - A Canadian teacher arrested in China for administrative reasons - a case officially unrelated to the ongoing diplomatic row between Beijing and Ottawa - has been freed, authorities said Friday (Dec 28).

Global Affairs Canada "confirms that a Canadian citizen, who was detained in China in December, was released and has now returned to Canada," spokesman Richard Walker said, without providing further details.

The arrest of Sarah McIver, a teacher accused of working illegally in China, was announced shortly after that of two other Canadian nationals: former diplomat Michael Kovrig, employed by think tank International Crisis Group (ICG), and Michael Spavor, a consultant on North Korea.

The two men, whom China arrested on Dec 10, were detained on suspicion of "harm to national security" - a phrase often used by Beijing when alleging espionage.

But many observers believe it was retaliation following the early December arrest in Vancouver of Chinese telecommunications giant Huawei's chief financial officer, Meng Wanzhou.

Ottawa has repeatedly said Meng's arrest was not political, but rather part of a judicial process in keeping with an extradition treaty with Washington.

Foreign Minister Chrystia Freeland did not mention the woman in calling for the release of the other two Canadians last week.

China's Foreign Ministry did not immediately respond to a request for comment. On Saturday, a Chinese court will hear an appeal in the case of a Canadian citizen held on drugs charges, that could further test the tense relations between the two countries.

The high court in the city of Dalian in the north-eastern province of Liaoning will hear the appeal of Robert Lloyd Schellenberg from 2 pm, it said in a statement this week.

A Dalian government news portal said Schellenberg was a Canadian and that this was an appeal hearing after he was found by an earlier ruling to have smuggled "an enormous amount of drugs" into China.

Canada's government said this week it had been following the case for several years and providing consular assistance, but could provide no other details, citing privacy concerns. Drugs offences are usually punished severely in China.

China executed a Briton caught smuggling heroin in 2009, prompting a British outcry over what it said was the lack of any mental health assessment.