Activists at Human Rights Watch told AFP that relatives of Muhammad Bekjanov -- jailed since 1999 -- confirmed he had been freed and was heading to the capital of the tightly- controlled Central Asian nation.
"They said he has been released and is on his way to Tashkent," said Hugh Williamson, the director of the group's Europe and Central Asia division.
Bekjanov's US-based daughter, Aygul Bekjan, wrote on Facebook that she was "happy" at her father's release but "so mad for the fact that he lost 18 years of his life for nothing!"
Bekjanov edited a prominent opposition newspaper in Uzbekistan until his arrest in 1999 on charges linked to a spate of bombings, with supporters insisting the case was designed to muzzle him.
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Uzbekistan has one of the most repressive regimes in the ex-Soviet Central Asian region dominated by strongmen leaders.
Bekjanov's release follows the death last year of veteran despot Islam Karimov -- who had led the country since independence in 1991.
Uzbekistan has released several prominent political prisoners since new leader Shavkat Mirziyoyev, a Karimov loyalist, took over as president.
Mirziyoyev, who served as prime minister for 13 years, has shown signs that he may be willing to open up the country's political system slightly, but a transition to democracy seems highly unlikely.
His original prison sentence was extended by nearly five years in 2012 and observers of the case feared that another extension was imminent following the switch.