Speaking in Sofia, U.S. Secretary of State Condoleezza Rice condemned what she called the "reprehensible action" of the government of Belarus.
The Organization for Security and Cooperation in Europe also called the sentence "unacceptable."
And in Brussels, European Commission spokeswoman Emma Udwin said the EC is watching the situation.
"We're following this extremely closely. We condemn any detentions that are [carried out] for reason of having taken part in a demonstration, or any other political activity."
The same Minsk court today gave another two opposition figures -- Popular Front leader Vintsuk Vyachorka and Labour Party chairman Alyaksandr Buchvostau -- similar jail sentences for taking part in yesterday's rally.
A fourth opposition leader, Syarhey Kalyakin of the Communist Party, received a 14-day administrative jail term.
(compiled from agency reports)
Belarus Votes 2006
MEET THE CANDIDATES: Read brief biographies of the four candidates in the March 19 election.