Police detained Russian opposition leader Garry Kasparov, the former world chess champion, and at least 100 other activists Saturday as they gathered for a forbidden anti-Kremlin demonstration in central Moscow. The so-called Dissenters' March increased tension between opposition supporters who complain the Kremlin is cracking down on political dissent and authorities who vow to block any unauthorized demonstrations. A similar march planned for St. Petersburg on Sunday also has been banned. Since the first such march in December in Moscow, Kasparov has emerged as one of President Vladimir Putin's most prominent critics. He has vowed to accelerate his protest actions as Russia draws nearer to presidential and parliamentary elections. Kasparov's United Civil Front organization works with other opposition groups in a loose alliance called Other Russia, which organized the marches.