Russia, Ukraine and other former Soviet states are colluding in an illegal rendition programme, a new report from Amnesty International has claimed.
The report says Russia and Ukraine have "stepped up" efforts to return people to Central Asian countries over the past two years.
That is despite there being European Court of Human Rights rulings blocking the extraditions, according to Amnesty.
The report says many people have been sent back to torture and unfair trials.
People from former Soviet countries have been abducted by foreign security forces and forcibly returned to Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan, according to Amnesty.
'Denials lack credibility'
Those targeted include people detained on charges related to national security, religious extremism, civil society activists, members of Islamist parties and groups and wealthy individuals who have fallen foul of the regimes.
Amnesty says over the past two decades, thousands of people across the region have been detained and tortured in custody in order to try to extract confessions or money from relatives.
The charity's director of Europe and Central Asia, John Dalhuisen, said public officials were complicit in the renditions.
"The authorities protest innocence and ignorance about abduction cases, but this lacks all credibility," he said.
"It is virtually impossible for a wanted individual to disappear on release from a prison in one country and reappear shortly afterwards in prison in another, without the involvement - or close co-operation - of the secret services of both countries."
Many of the countries cited in the Amnesty report have been condemned for their poor human rights records.
Uzbekistan is notorious for its treatment of prisoners.
Leading human rights campaigner Mutabar Tadjibaeva was released from prison in Uzbekistan in 2008, after being sentenced to serve an eight-year sentence after accusing the government of shooting unarmed protesters in the city of Andijan in 2005.
She told the BBC how she spent two years and eight months in custody.
"One hundred and twenty days of that was in solitary confinement throughout the winter with open windows, without warm clothes. They tortured me with hunger and other methods too.
"And last they cut out my womb without my consent.
"Before I went to prison, I was a completely healthy woman. Now I'm disabled."
Amnesty said it was unusual for extradition requests to be rejected in the region as "good relations and the perceived mutual interest in combating terrorism nearly always comes before the human rights of individuals wanted for extradition".