But given the routine dispersal by police of even small rallies in recent months, organisers decided against major protests this year and wanted instead to hand in a petition.

"Citizens of Belarus demand to know what the authorities are doing to solve the problems of Chernobyl," read the petition, read out by activists outside the presidential administration.

Police seized about 15 of the 300 protesters after they unfurled a banner reading "Today Ukraine, tomorrow Belarus!" -- referring to last year's "Orange Revolution" protests which led to the election of liberal president Viktor Yushchenko.

About 10 activists of Russia's liberal Union of Right Forces party were detained before the rally, a party official said.

Demonstrators were demanding an end to efforts by Lukashenko's government to persuade villagers to return to resettle areas affected by the April 26, 1986 explosion in Chernobyl's fourth reactor -- the world's worst civil disaster.

Some Western commentators have suggested that Belarus might be the next ex-Soviet state to fall under the influence of pro-democracy protests after mass rallies forced government changes in Georgia, Ukraine and Kyrgyzstan.

But Lukashenko has tightened his grip and vowed no such upheaval will occur in his country of 10 million wedged between Russia and new EU members Poland, Latvia and Lithuania.