Kazulin's spokeswoman, Nina Shydlouskaya, said he is now being held in a Minsk police station after suffering a severe beating.
In other developments, the leading opposition presidential candidate in Belarus has called a preelection rally later today in the capital, Minsk, without permission from authorities.
Alyaksandr Milinkevich said if police use force to break up today's rally, the opposition "reserve the right to take appropriate measures." He gave no explanation of what these measures might be.
The head of Belarus's Central Election Commission, Lidziya Yarmoshyna, has called the planned rally a "provocative act" and said security forces are entitled to use force.
MEET THE CANDIDATES: Read brief biographies of the four candidates in the March 19 election.