China is accused of locking up hundreds of thousands of Muslims without trial in its western region of Xinjiang.
The government denies the claims, saying people willingly attend special “vocational schools” which combat “terrorism and religious extremism”.
Now a BBC investigation has found important new evidence of the reality.
On 12 July 2015 a satellite swung over the rolling deserts and oasis cities of China's vast far west.
One of the images it captured that day just shows a patch of empty, untouched, ashen-grey sand.
It seems an unlikely place to start an investigation into one of the most pressing human rights concerns of our age.
But less than three years later, on 22 April 2018, a satellite photo of that same piece of desert showed something new.
A massive, highly secure compound had materialised.
It is enclosed with a 2km-long exterior wall punctuated by 16 guard towers.
View attachment 507332View attachment 507332The first reports that China was operating a system of internment camps for Muslims in Xinjiang began to emerge last year.
The satellite photograph was discovered by researchers looking for evidence of that system on the global mapping software, Google Earth.
It places the site just outside the small town of Dabancheng, about an hour's drive from the provincial capital, Urumqi.
To try to avoid the suffocating police scrutiny that awaits every visiting journalist, we land at Urumqi airport in the early hours of the morning.
But by the time we arrive in Dabancheng we're being followed by at least five cars, containing an assortment of uniformed and plain-clothes police officers and government officials.
It's already clear that our plan to visit a dozen suspected camps over the course of the next few days is not going to be easy.
s we drive up the wide approach road we know that sooner or later the convoy behind is going to try to stop us.
While still a few hundred metres away, we see something unexpected.
The wide expanse of dusty ground, shown on the satellite image to the east of the site, is empty no more.
In its place, a huge extension project is taking shape-
Like a mini-city sprouting from the desert and bristling with cranes, are row upon row of giant, grey buildings - all of them four storeys high.
With our cameras rolling we try to capture the extent of the construction, but before we can go much further one of the police cars swings into action.
Our car is stopped - we're told to turn off the cameras and to leave.
But we've discovered something of significance - a huge amount of extra activity that has so far gone unnoticed by the outside world.
In remote parts of the world, Google Earth images can take months or years to update.
Other public sources of satellite photography however - like the European Space Agency's Sentinel database - provide much more frequent images, although they're of a much lower resolution.
It is here that we find what we are looking for.
ZedRef- BBC