Bolatbek Beldibekov, the head of the local police department’s press service, told the newspaper Uralskaya Nedelya that the offense was not that he demonstrated with the blank placard. Rather, he said, Mr. Sagutdinov ran afoul of the law by making the political statement that “there is no democracy and free speech in Kazakhstan” in a public place.

The episode stood out to human rights watchers as a particularly vivid example of Kazakhstan’s restrictions on expression.

On Thursday, as demonstrations were planned on the country’s May 9 Victory Day holiday, several major local and international news publications were blocked, and citizens reported that access to Facebook was restricted. One news publication, Vlast, wrote on Facebook that one of its correspondents, Daniyar Moldabekov, was detained by the police despite showing officers his press badge. He was later released.

Kazakhstan’s Constitution grants its citizens “the right to peacefully and without arms assemble, hold meetings, rallies and demonstrations, street processions and pickets.” But it also allows for restrictions on those rights, and activists say those restrictions have been extensive.

“These authorities are very, very creative in using these provisions of administrative law,” said Yevgeniy Zhovtis, director of the Kazakhstan International Bureau for Human Rights and Rule of Law.

Those seeking to publicly demonstrate, either in groups or by themselves, must apply to local officials 10 days in advance, he said. If approved — and many applications are not — the protests will be confined to a few designated areas, he said.

Mihra Rittmann, senior Central Asia researcher for Human Rights Watch, said at least four other people had been detained in the past month for expressing their views publicly, even when the messages did not oppose the government. In one case, an artist was charged with “petty hooliganism” after hanging a banner over a highway with a quote from the Constitution.