China has accused the detained Canadian citizen Michael Kovrig of stealing state secrets, in the latest escalation of tension between the two countries after Canada approved the extradition of the senior Huawei executive Meng Wanzhou to the US.

Chinese authorities said Kovrig, who has been in detention in China since December, was passed intelligence by the Canadian businessman Michael Spavor, according to a statement released on Monday night by the Chinese Communist party’s central political and legal affairs commission. Spavor has also been in detention since December.

The statement said Kovrig, a former diplomat, had often entered China using an ordinary passport and business visas, “stealing and spying on sensitive Chinese information and intelligence via a contact in China”.

“Kovrig’s actions, suspected of stealing, spying on state secrets and intelligence, have seriously violated Chinese law,” the commission said, describing Spavor as his “main contact”.

On Friday, Canada’s justice department approved the beginning of extradition proceedings for Meng, who has filed a civil lawsuit against Canada over her arrest. She is free on bail and denies the charges against her.

Kovrig and Spavor, a businessman with North Korean ties, were detained on 10 December, 10 days after Canadian police arrested Meng at the request of the US, where she faces charges of bank and wire fraud and violating US sanctions against Iran.

Canadian diplomats have been allowed to see the two men. People familiar with the case have said Kovrig has not been allowed access to lawyers or family members, unlike Meng. Kovrig, who works for the International Crisis Group, focusing on north-east Asia, has denied any involvement in espionage.

The Canadian prime minister, Justin Trudeau, said: “We are obviously very concerned by this position that China has taken. It is unfortunate that China continues to move forward on these arbitrary detentions.”

China has repeatedly demanded Meng’s release and said Ottawa’s decision last week amounted to a “severe political incident”.

Canada said China had not made a specific link between the detentions and Meng’s arrest, but experts and former diplomats believe Beijing is using their detentions as a way to put pressure on Canada. In January, a Chinese court retried the Canadian Robert Schellenberg on drug-trafficking charges and increased his sentence from 15 years in prison to the death penalty.

The Chinese commission said on Monday the next judicial proceedings would begin in due course and stressed that Kovrig’s and Spavor’s “lawful rights would be ensured”.

“China is a country with rule of law and will firmly crack down on criminal acts that severely undermine national security,” it said.