The case comes as Beijing and Ottawa remain embroiled in a diplomatic row triggered by Canada’s December 1 arrest of a senior executive from Chinese telecommunications giant Huawei wanted in the United States.

In what observers see as an act of retaliation, China later detained two Canadians — a former diplomat and a business consultant — on suspicion of engaging in activities that “endanger” national security.

In a previous ruling in November, Schellenberg was sentenced to 15 years in prison and a 150,000 yuan (US$22,000) forfeiture.

The high court in northeastern Liaoning province, which presided over Schellenberg’s appeal attempt last December, called the sentencing “obviously inappropriate” given the severity of his crimes.

Schellenberg played “an important role” in drug smuggling and was potentially involved in international organised drug trafficking activities, it said.

Other foreigners have been executed for such crimes.

In 2014, a Japanese national sentenced in Dalian city in northeastern Liaoning province was put to death for drug offences, according to Tokyo diplomats and media reports.

China also sentenced a Filipina drug trafficker to death in 2013, according to the Philippine foreign department, ignoring Manila’s request to spare her life.