Canada's Foreign Minister Melanie Joly told reporters in Ottawa on Wednesday that China had executed four Canadian citizens in recent weeks, defying pleas from Ottawa for leniency.

"We strongly condemn the executions that did happen against Canadians in China," Joly said.

She said she was unable to discuss details of the case due to privacy requests from the affected families.

However, Beijing suggested on Thursday the Canadians had been convicted over narcotics offences, saying "... combating drug crimes is the common responsibility of all countries".

"China is a country under the rule of law," foreign ministry spokeswoman Mao Ning said.

Beijing, she said, "treats defendants of different nationalities equally without discrimination" and "handles cases fairly in strict accordance with the law".

China "protects the legitimate rights of the parties concerned as well as the consular rights of the Canadian side, in accordance with the law", Mao said.

Beijing also defended the executions in a statement sent to Canada's Globe and Mail newspaper.

"Drug-related crime is a severe crime recognised worldwide as extremely harmful to the society," the embassy statement said.

"China always imposes severe penalties on drug-related crimes and maintains a 'zero tolerance' attitude towards the drug problem."

Joly said she and former prime minister Justin Trudeau, who left office last week, had asked China for leniency.

China classifies death penalty statistics as a state secret, although rights groups including Amnesty International believe thousands of people are executed in the country every year.

Beijing said this week a former Chinese engineer had recently been sentenced to death for leaking state secrets to a foreign power.

Relations between Beijing and Ottawa have been tense in recent years.

The arrest of a senior Chinese telecom executive on a US warrant in Vancouver in December 2018 and Beijing's retaliatory detention of two Canadians on espionage charges plunged relations into a deep freeze.

Ties were strained further over allegations of Chinese interference in Canadian elections in 2019 and 2021, charges Beijing has denied.

Joly expelled a Chinese diplomat in 2023 accused of targeting a Canadian opposition lawmaker who has been a vocal critic of the ruling Communist Party in Beijing, as well as his family.

Ottawa has also criticised a security crackdown in Hong Kong and China's treatment of its Uyghur Muslim minority.