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

At least 250 people were detained by police at a protest in downtown 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 another 25 in the southern city of Rostov-on-Don.

It was the second consecutive night of large protests in Moscow and St. Petersburg, an unusually sustained show of indignation as 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.