Image copyright Reuters Image caption Nobel Prize laureate Liu Xiaobo was convicted of subversion in 2009

China's Communist rulers are trying to force the country's jailed Peace Prize laureate into going into exile by putting pressure on his wife, who is not well, the BBC has been told.

A source close to the family has told us that Liu Xiaobo will not agree to leave China as that would lead to his voice being marginalised.

But the source said that Liu Xiaobo's wife Liu Xia is "suffering mentally" because she has now spent two years under illegal house arrest and continues to be detained.

It was exactly two years ago when Liu Xiaobo, a soft-spoken academic, won the Peace Prize for his calls for peaceful political reform in China.

He never collected it as he was already in a jail in China, where he remains, convicted of subversion.

His wife Liu Xia, an even softer-spoken poet and photographer, has been similarly silenced. She's being held in her own flat in Beijing.

She's been there for two years, detained just a couple of days after her husband was announced as the 2010 winner.

And Norway too is, it seems, still being punished. The prize has nothing to do with the Norwegian government.

But China continues to snub Norwegian ministers, diplomats and politicians, according to other diplomats in Beijing.

Liu Xia effectively ceases to exist, both as a human being and as an issue Joshua Rosenzweig, Human rights expert

Tight control

But the BBC has spoken to an individual in contact with Liu Xiaobo and Liu Xia's families, who has given some new insights into the couple's situation.

The individual asked that we don't name them, and told us that Liu Xiaobo is in reasonable health, but his stomach problem "is getting worse".

China's authorities allow only three people to visit Liu Xiaobo in Jinzhou prison where he's being held: his two brothers who can see him about once every six months, and his wife who sees the Nobel Peace Prize winner every two to three months, the source said.

They have to ask for permission in advance and wait for notification.

"They are not allowed to go and visit him together. Only one person is allowed each time. And the police watch them during the entire meeting," our source told us.

"They are forbidden to talk about anything else other than family matters. The police don't want the family to bring in any information from outside to Liu Xiaobo."

The two brothers did visit together once, in September last year. That was to inform Liu Xiaobo that his father had died. He was then allowed a brief visit home to pay his respects before he was whisked back to jail.

His wife, Liu Xia, meanwhile, has not committed any crime in China but is being held in her home.

"There are two policewomen living with her in her apartment. And lots of plain-clothes police watching the compound constantly," our source told us.

Image copyright Getty Images Image caption Liu Xia's latest photo exhibition, on display in Hong Kong, focuses on the suffering of Chinese people

"Liu Xia's health is not very well. Mentally she suffers a lot because of the loss of personal freedom and the worries about her jailed husband."

"She is allowed to go out and visit her mother and meet one of her best friends roughly once a month, escorted by policewomen the entire time. Other than visits to her husband, that's it.

"She is not allowed to go anywhere else, not even to the park or shop. And no-one is allowed to even approach her compound, let alone visit her."

The individual added: "What the government is doing to Liu Xia is illegal. They do this routinely to dissidents in order to prevent them speaking to the press and tainting the government's image.

"Her husband is currently the most famous dissident in China, so she suffers tighter control than other dissidents."

'Very cruel'

His view is backed up by Joshua Rosenzweig, a human rights researcher at the Chinese University of Hong Kong who said he was "not aware of any legal authority for restricting Liu Xia's liberty".

"Her relegation to this ambiguous zone appears to be deliberate, because if you can't treat [her detention] as something sanctioned or even covered by law, then how do you begin to challenge it? Liu Xia effectively ceases to exist, both as a human being and as an issue," he said.

The government wants Liu Xiaobo to leave because the fact that a Nobel Peace Prize winner is in jail is a reminder of China's poor human rights situation Friend of Liu Xiaobo's family

China's government insists Liu Xia is not being held against her will. But Mr Rosenzweig says its aim is to silence Liu Xia, her husband and their families, so there is no news about the jailed laureate.

"One of the few ways the outside world has to learn anything about individuals who have been imprisoned in China is through what their relatives learn and observe during periodic prison visits," he says.

"I don't know the last time that Liu Xia was able to visit her husband, but I am fairly certain that any interaction she has been able to have with him has been under the precondition that she remain silent.

"To the extent that this reflects an official strategy to counter Liu Xiaobo's influence, it would have to be deemed successful. There's only so much interest that can be sustained by a person's continued absence.

"That's why you don't see too many headlines proclaiming 'no news of Nobel laureate again this month'."

And the friend of the family who spoke to the BBC says that, by being so harsh on his wife, China is trying to pressure Liu Xiaobo into cutting a deal to go into exile.

"The government is trying to force Liu Xiaobo to leave China by taking his wife's personal freedom away. At the same time, the government threatens both their families, saying if they try to speak to the media or leak any information their right to visit Liu Xiaobo will be taken away.

"This is very cruel. It has forced the family to keep quiet."

But, the family friend added, Liu Xiaobo will not agree to leave China, despite the fact that his prison term lasts until 2020.

"The government has always wanted Liu Xiaobo to leave China because the fact that a Nobel Peace Prize winner is in jail, is a constant reminder of China's poor human rights situation.

"When previous dissidents have left China their voices gradually fade and their influence disappears. That's why Liu Xiaobo insists he'll stay even if it means staying in jail. Remaining in China is what's significant for him."