China is pressuring Uyghurs living abroad to spy on human rights campaigners by threatening families back home, researchers say. Refugees and activists tell the BBC intimidating tactics are tearing communities apart.

"My dearest son," said Alim's mother as she flickered into view. "I didn't think I'd see you before I died."

Alim - not his real name - says he was overcome by the moment. The reunion over a video call was their first contact in six years, since he fled as a refugee to the UK.

But it was bittersweet: someone else was in control of the call. Like all Uyghurs - a mostly Muslim minority from north-western China - Alim's mother lives under intense surveillance and control. They could never call each other directly.

Instead, a middleman phoned Alim and his mother from two separate mobiles. He held the phone screens to face each other, so the pair could see wobbly images of each other - and hear muffled sound from the speakers.

Alim says they barely spoke, and spent most of the call in tears.

He doesn't know if the plain white wall he could see behind his mother was in her house in Xinjiang or an internment camp, where the Chinese government is alleged to have detained more than a million Uyghurs. China has long denied those charges.

But Alim says he knew this contact with his mother would come at a cost - because the man brokering the call was a Chinese police officer.

When the officer called again, he asked Alim to attend meetings of Uyghur human rights activists, gather intelligence and pass it back to the Chinese state.

"Whenever there was an anti-China protest in London, they would call me and ask who would be attending," says Alim, who shared with the BBC recordings of the phone calls requesting he work as a spy.

Alim was offered money, too, so he could try to befriend the leaders of campaign groups - many of them UK citizens - by taking them to restaurants and picking up the bill.

The officer suggested setting up a company as a front, in case suspicions were raised about his newfound wealth. Plenty of businesses had already been set up on behalf of others for that exact purpose, Alim was told.

The implied threat, that his family may come to harm if he refused, has left him in a vicious bind.

"They are using my family as hostages," Alim says. "I am living in a dark moment."

Research suggests this particular kind - controlling access to family members in the home country through video calls, in exchange for compliance overseas - is commonly used by Chinese police.

Dr David Tobin at the University of Sheffield has conducted some of the most comprehensive research on the topic to date, with his colleague Nyrola Elimä. They have interviewed and surveyed more than 200 members of the Uyghur diaspora in several countries. He says all Uyghurs living outside China are victims of transnational repression.

"Family separation is the central tactic," he says. Even where phone calls are technically possible, relatives still living in China won't pick up, according to Dr Tobin. He says there is an assumption that calls will be monitored, and a fear that communicating freely will put them at risk.

This severing of family ties allows Chinese police to step in and offer tightly managed access - over video calls - as an incentive to comply, with the threat of repercussions for the family if they do not.

In the UK, Dr Tobin surveyed or interviewed 48 Uyghurs, from a population of about 400 people. Of those, two-thirds reported having been contacted directly by Chinese police - and pressured to spy, refrain from advocacy work, or stop speaking to the media.

And Uyghurs in the UK are far from the worst affected.

In Turkey, traditionally a safe haven for Uyghurs where 50,000 live in one of the largest communities outside China, 80% of the 148 of respondents reported similar threats from Chinese authorities.

Abdurehim Paraç arrived in Istanbul in 2014, having fled China a year earlier.

"Turkey was completely different to anything we'd experienced. We could travel wherever we wanted. The police didn't bother us," he says. "I couldn't believe such a life was possible."

But in the past few years, the picture has changed for Uyghurs in Turkey. Reports that police based in China have pressured people to spy on each other have filtered through the community, splintering their sense of camaraderie.

In a video posted on Facebook, a young Uyghur man who appears to have been captured and beaten by his peers, offers a troubled confession - admitting to spying on behalf of Beijing. While the circumstances surrounding the scene are unclear, the footage has been circulated among the Uyghur community, and the man has been widely condemned online.

The accumulation of stories like these is having an effect, Abdurehim says.

"Young people are distancing themselves from Uyghur protests and meetings. They are worried that people there might be spies," he says. "China's plan is working."

Dr Tobin thinks Turkish authorities are aware of what's happening and have been slow to respond. "The more dependent a country is on investment from China, the more likely it is to cooperate or to turn a blind eye," he says.

Turkey is seen as having grown closer to China in recent years, and questions have been raised about its commitment to protecting its Uyghur community.

The Turkish government did not respond to a request for comment.

But China is not only targeting people in countries where it has economic supremacy.

Julie Millsap, a US-born activist who works with the Uyghur Human Rights Project in Washington DC, says China has tried to pressure her through her in-laws.

Her husband is Han Chinese, part of the country's largest ethnic group, and the two met in China before moving to the US capital in 2020.

After Julie began campaigning on behalf of Uyghurs, local police began dropping in on her extended family in China, saying they "wanted to be friends".

She and her husband received threatening messages from her sister-in-law's phone, suggesting Julie's children may end up "as orphans". "They weren't written in a language style that she used," says Julie, who suspects the police were instructing her to send them.

During a recent video call between her husband, in Washington DC, and his sister, in China, the police happened to stop by, allowing Julie to record the moment, and confront one of the officers directly.

"He stammered and asked us not to misinterpret his intentions," she says. The officer told her police were arranging visits to all local families with US relatives, in light of the "delicate" relationship between the US and China.

Julie recognises that a white American and a Han Chinese family are afforded a degree of safety that Uyghurs are not. "But we're still talking about police harassment, about threats, about a daily reality that is anything but good," she says.

She thinks it is alarming that Chinese authorities feel comfortable targeting foreign citizens and attempting to dictate their work.

The US government is beginning to address the problem formally.

In March, senators introduced the Transnational Repression Policy Act, listing a range of abuses including "coercion by proxy", which covers threats to family members overseas. If passed, the law would see the creation of a dedicated phone line to report threats, and prompt Congress to bring sanctions against perpetrators wherever possible.

Abduweli Ayup, a Uyghur rights campaigner based in Norway, thinks the US legislation would be a step in the right direction, but that Western governments should go further. Each time a case is reported to the authorities, questions should be lodged directly with the Chinese government, requesting assurance that family members are safe, he says.

"We are your citizens, your neighbours and your taxpayers. Our governments should take some responsibility," says Mr Ayup.

Dr Tobin recognises the complications inherent in tackling the issue. "Saying 'would you like to speak to your family?' isn't a crime. We know it's a threat. We know it breaks communities, and causes mental health problems and trauma, but it is not a crime on British soil," he says.

The UK Home Office says attempts to intimidate overseas critics are "unacceptable", that an internal review into transnational repression is underway, and all such incidents should be reported to law enforcement.

In a statement, the Chinese Embassy in London called the allegations of transnational repression "totally groundless". The Chinese government "protects Uyghurs and their communication with overseas relatives in accordance with the law", it said.

Alim chose not to report his case to the police, but confessed his predicament to a group of Uyghur rights activists in London.

One of the group's leaders told us the requests were very common, and posed challenges to the integrity of the community - but insisted their advocacy work would continue. In their experience, almost all advances from Chinese police are rejected.

Alim wrestled with the issue before reaching a decision. "I realised that betraying others for the sake of my family would mean selling out my nation, and I couldn't do that.

"If that was the price I had to pay, so be it." He too refused China's offer.