The three countries accuse Belarusian authorities of waging a campaign to shut down civil society, independent media and any form of political opposition.
"We - Australia, Canada, and the United Kingdom - stand united in condemning the ongoing repression and human rights violations," they said in a joint statement.
"Thousands have been unjustly detained, subjected to torture, or forced into exile. These actions represent a flagrant breach of Belarus' international law obligations and are a serious violation of human rights and fundamental freedoms," they added, urging Belarusian authorities "to end their campaign of repression."
Belarusian President Alexander Lukashenko, a close ally of Russian President Vladimir Putin, has led Belarus through more than three decades of authoritarian rule and was re-elected in January for a seventh five-year term.
Lukashenko crushed huge street protests in 2020 after an election the opposition and Western governments accused him of stealing, and all his leading opponents were jailed or forced to flee the country.
Several hundred people convicted of extremism and other politically related offences have been released since mid-2024 in what analysts see as a bid by Lukashenko to ease his isolation from the West. However, human rights groups say nearly 1200 are still behind bars.
Lukashenko denies there are any political prisoners in the country.
Australia, Canada and the UK said they welcomed the recent releases of several political prisoners in Belarus but added that they remain concerned by what they termed as continued arrests and persecution of individuals for exercising their human rights.
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