The Central Asian state of Uzbekistan is a serious threat to itself and to the region, the International Crisis Group (ICG) has warned in a report.
Mr Karimov's is considered one of the region's most autocratic leaders
The human rights situation is grave, and the regime's critics are severely persecuted, the think tank said.
The eventual departure from office of President Islam Karimov, whose latest term ended in January, could lead to a violent power struggle, it warned.
However, there is little outsiders can do to influence the situation, it said.
The government cites the dangers posed by radical Islamist groups to justify its repressive policies, but there is no clear evidence they pose a threat, the report said.
The group warned that support for radicalism could grow as a result.
"The political scene is full of uncertainty," Robert Templer, the think tank's Asia director said.
"The apparent public apathy reflects not support for the regime but rather pervasive fear and a sense of hopelessness.
"There is great resentment, increasing the chance of serious unrest whose impact will be felt throughout Central Asia once Karimov steps down," he said.
The EU recently renewed sanctions imposed in 2005 after Uzbek troops fired on protesters in the eastern town of Andijan.
Uzbekistan said that decision was unfounded, biased and an "instrument of systematic pressure... dressed up in human rights rhetoric".
The ICG is a non-governmental organisation that works through field-based analysis and high-level advocacy to prevent and resolve conflicts.