In less than two weeks, the Central Asian nation has released two dissidents imprisoned under the previous president, Islam Karimov, while detaining two others.
The releases have been welcomed by the West, but the New York-based Human Rights Watch said the fresh arrests 'cast a pall over what would otherwise be a sign of hope.'
Human rights activist Azam Farmonov was freed on Tuesday after 11 years in prison and Solijon Abdurakhmanov, a journalist imprisoned since 2008, was released on Wednesday.
They joined a string of Karimov-era political prisoners set free by his successor, Shavkat Mirziyoyev, who took power in the mostly Muslim nation of 32 million people following his autocratic predecessor's death in September 2016.
Mirziyoyev, who seeks to attract foreign investment to modernize Uzbekistan's Soviet-style economy, has ordered some 16,000 people struck off a blacklist of potential extremists and dissidents and taken other steps to liberalize the country.
But when one of those dissidents, prominent writer Nurulloh Muhammad Raufkhon, returned from exile last month, he was detained and charged with spreading anti-government propaganda.
The writer was later released but still faces the charges.
Another dissident, Bobomurod Abdullayev, a journalist accused of publishing stories critical of the government on an opposition website, was also arrested and charged last month. He remains in detention.
'The release of Azam Farmonov and Solijon Abdurakhmanov after long years of abuse was positive news, but there should be no revolving door for political arrests,' said Steve Swerdlow, Central Asia researcher at Human Rights Watch.
'President Mirziyoyev should see to it that all political prisoners are released and that all of Uzbekista's citizens are guaranteed the fundamental right to peacefully express critical opinions.'
In Raufkon's case, Uzbek police have said that while he may have been struck off the blacklist, the charges against him - leveled in absentia in May - were never dropped and he did not contact authorities about them before returning to Uzbekistan.
Police have not commented on Abdullayev's status.