MOSCOW - Police clashed with demonstrators protesting alleged election fraud in Moscow and at least two other major Russian cities Tuesday as anger boiled over against strongman Prime Minister Vladimir V. Putin and his United Russia party.

At least 250 people were detained by police at a protest in Moscow that included flare-type fireworks thrown at a group of pro-Kremlin youth, said city police spokesman Maxim Kolosvetov.

Russian news agencies reported about 200 were arrested at a similar attempt to hold an unsanctioned rally in St. Petersburg and 25 in the southern city of Rostov-on-Don. The Moscow protest ended after about 31/2 hours and the others were broken up by police.

It was the second consecutive night of large protests in Moscow and St. Petersburg, an unusually sustained show of indignation. Russian police routinely crack down hard on unauthorized rallies, and protesters generally take time to regroup for a new attempt.

The demonstrations follow Sunday's parliamentary election, in which United Russia lost a large share of the seats it had held in the State Duma. The party maintains a reduced majority, but opponents say even that came because of vote fraud.

Local and international election observers reported widespread ballot-stuffing and irregularities in the vote count.

The protesters appear to be angered by the reported fraud and energized by the vote's show of declining support for Putin and his party, which has overshadowed all other political forces in Russia for the last dozen years.

But pro-Kremlin supporters also put on a pair of large rallies in Moscow, attracting thousands and showing strong divisions in Russian society.

The Moscow protest demonstrated the violent potential of those divisions.

A heavy police presence was visible throughout the city, including several police trucks parked around Pushkin Square, another popular demonstration site.

United Russia won slightly less than 50 percent of Sunday's vote, according to nearly complete preliminary results. Although that gives the party an absolute majority in the State Duma, the lower house of parliament, it is a significant drop from the 2007 election when the party got a two-thirds majority, enough to change the constitution unchallenged.

Sunday's election results reflect public fatigue with Putin's authoritarian streak and with official corruption in Russia, signaling that his return to the presidency in March's election might not be as trouble-free as he expected.

The Russian election even drew criticism from one of Putin's predecessors.

"There is no real democracy here and there won't be any, if the government is afraid of the people," former Soviet leader Mikhail Gorbachev said on Ekho Moskvy radio.