An EC spokeswoman urged the Belarusian authorities to immediately release the opposition leader and suggested the EC could impose new sanctions against the country, though she did not specify what this would mean.
Police detained Milinkevich, who ran unsuccessfully in the country's presidential election in March, earlier on Thursday at the editorial office of an independent business weekly and a Minsk court handed him down a 15-day sentence for taking part in an unauthorized demonstration.
On Wednesday, the opposition organized a 3,000-strong rally timed to coincide with the 20th anniversary of the Chernobyl disaster, the world's worst nuclear accident, which affected much of the country. Protesters held Ukrainian and EU flags, chanted "Long Live Belarus!" and "Freedom!" and expressed support for Milinkevich.
Presidential elections held March 19 in the former Soviet republic that saw Alexander Lukashenko reelected to a third term with 83% of the vote were condemned as undemocratic by international monitors.
The opposition also said the poll was rigged, and pledged to continue protests.
