China’s ambassador to Australia has labelled reports that one million Uighurs are being held in detention “fake news”, seeking to excuse mass incarceration as a deradicalisation measure.

At a rare press conference at the Chinese embassy in Canberra, Cheng Jingye claimed the mass detention in Xinjiang province had “nothing to do with human rights, nothing to do with religion” and was “no different” from other countries’ counter-terrorism measures.

Cheng also defended China’s detention of Australian writer Yang Hengjun, claiming that his health is good and his rights are being protected, despite the fact he has not had access to his lawyers.

Asked about Australia foreign minister Marise Payne’s criticism of the mass detention of Muslim Uighurs – a fact established by leaked Communist party documents – Cheng responded that “Xinjiang-related matters are internal affairs of China”.

He claimed that reports that 1m Uighurs are in detention are “utterly fake news” and then played a propaganda video to argue the measure was a response to 20 years of violence in Xinjiang province.

“Those attacks and violence … [claimed] a large number of innocent people and also … brought huge damage to property,” he said.

“The local government has taken tough measures to crack down on those [instances of] terrorism or violence.

“At the same time, they have started to take measures to address the fundamental causes of those attacks.”

Cheng said the detention camps were education centres “aimed at deradicalisation” and taught those of “extremist origin” vocational skills, including legal knowledge and the Chinese language.

“I think the number of trainees [is] dynamic. Some of them came in, some went out.”

Cheng said since the re-education efforts the spread of extremism had “been effectively curbed” and “there have been no single violence or terrorist cases in the past three years”.

“So what has been done in Xinjiang has no … difference with what the other countries, including western countries, [do] to fight against terrorists.”

Cheng ducked a question about why China did not allow international observers into the camps, suggesting that internees – who he called “trainees” – went on to resume work and “live a normal life”, echoing claims by Xinjiang’s governor.

Satellite photos have revealed that dozens of cemeteries in the north-western region of China have been destroyed in the last two years, as well as the demolition of Islamic religious sites.

Cheng said there were 20,000 mosques and 29,000 Islamic clerical personnel in Xinjiang, and claimed internment camps had “nothing to do with religion”.

Earlier in December, leading Uighur activist Rushan Abbas visited Australia to urge MPs to do more to speak up against the mass detention of Uighurs, which she labelled the “unprecedented atrocity of the century”.

Cheng confirmed that Yang Hengjun, detained in Guangzhou in January, was only formally arrested in August and is being held on suspicion of espionage.

Cheng said the case is still under investigation and “in due course [Yang] will be formally charged” – later backtracking to suggest that because the investigation is not complete it is also possible he will not be charged.

Guardian Australia has reported that Yang is granted one half-hour consular visit each month but has not been allowed to communicate with his lawyers, after nearly 11 months in detention.

For some of his incarceration, he had been subjected to a single interview each month during which he was not shackled, but earlier in December Yang was subjected to daily interrogation sessions, sometimes commencing at midnight, while his wrists and ankles were held in chains.

Cheng said he did not accept claims Yang is being subjected to daily interrogations with his arms and legs shackled.

Cheng deflected questions about why China has not invited Scott Morrison to visit, claiming that both countries are trying to facilitate “high-level exchanges and visits”.