A Chinese court has sentenced the Swedish bookseller Gui Minhai to 10 years in prison for “providing intelligence” overseas, deepening diplomatic tensions as Sweden demanded that China release him.

A court in Ningbo, an eastern port city, said on Tuesday that Gui had been found guilty and would be stripped of political rights for five years in addition to his prison term. The brief statement said Gui had pleaded guilty and would not be appealing against his case.

The Swedish foreign minister, Ann Linde, told Radio Sweden: “We have always been clear that we demand that Gui Minhai be released so he is able to reunite with his daughter, his family and that demand remains.

“We demand immediate access to our Swedish citizen in order to give him all consular support that he is entitled to.”

Gui, a Chinese-born Swedish citizen, ran a Hong Kong publishing house that acquired the independent bookstore Causeway Books, popular for gossipy titles about China’s political elite.

He was one of five people associated with the store who disappeared in 2015, in a case that rippled across Hong Kong, prompting fears about China’s growing grip over the city where the publishing industry had long enjoyed freedoms granted under the “one country, two systems” framework.

Authorities at first said Gui, who disappeared from his holiday home in Thailand, had been detained on suspicion of illegal business operation.

“We all know despite the government’s changes in charges, the real reason for Gui’s ordeal is that he has published books critical of the Chinese leadership,” said Yaqiu Wang, China researcher for Human Rights Watch.

Gui was held incommunicado for months before reappearing in 2016 in mainland China on state television, where he said he had turned himself in over a drink-driving incident that took place a decade earlier. Many human rights observers believed he had been coerced into making the statement.

He was partially released in 2017 but barred from leaving the country. In January 2018, he was detained by plainclothes officers while travelling with two Swedish diplomats to a medical appointment.

Weeks later, Gui reappeared during a press conference arranged by the government to say that Sweden had “sensationalised” his story and tricked him into an attempt to flee China for Sweden, in another confession that friends and rights advocates believe was forced.

“I fell for it,” he said. “My wonderful life has been ruined and I would never trust the Swedish ever again.”

Gui’s sentencing comes as global attention is focused on the coronavirus outbreak. China often announces the verdicts for dissidents and other sensitive figures when western audiences may be distracted, such as over Christmas.

“Gui appears to have been tried and convicted in secret, denying him any chance of a fair trial,” said Patrick Poon, a China researcher at Amnesty International, calling the verdict “deplorable” and based on unsubstantiated charges.

“Gui Minhai has all along been kept by the Chinese authorities after he went missing in Thailand in 2015. Illegally providing intelligence to foreign entities? How could he do that?”

In November, Swedish Pen awarded Gui the Tucholsky prize – named after the German writer Kurt Tucholsky who fled Nazi Germany for Sweden – for persecuted writers. China said Sweden would “suffer the consequences”.

The court in Ningbo acknowledged Gui had become Swedish in the 1990s but added that he had applied to restore his Chinese citizenship in 2018. China does not recognise dual citizenship and restoring his Chinese passport may have been a way to block Swedish diplomats from visiting him, observers said.

Critics say there have also been efforts to silence his daughter, Angela Gui, who has been lobbying for his release.

Anna Lindstedt, Sweden’s former ambassador to Beijing, is being investigated after she brokered an unauthorised meeting between Angela Gui and two Chinese men who claimed to be able to release her father. The men used the meeting to pressure her to stop speaking out, according to a blogpost.

Michael Caster, a human rights advocate and co-founder of the human rights organisation Safeguard Defenders, said: “If you want to understand the extent of human rights abuses perpetrated by China, Gui Minhai’s case is brutally emblematic.”

Gui, born in Ningbo, spent his 20s in Beijing in the 1980s before the Tiananmen protests, writing poetry published in pamphlets handed out during that rare window of openness and debate. He later moved to Gothenburg to study and became a Swedish citizen.

After moving back to China, and later to Hong Kong in the early 2000s, he entered the publishing industry and wrote several books under a pen name.

Amid anti-government protests that have rocked Hong Kong for most of the past year, the booksellers’ cases are often cited as an example of the city’s quickly eroding freedom under Chinese control.

The other four booksellers, who also gave confessions broadcast by state media, were eventually released. Before he disappeared in 2015, Gui was reportedly preparing to publish a book about the love life of the Chinese leader Xi Jinping.