MOSCOW, May 6 (Xinhua) -- An opposition rally was held here Sunday against Russian President-elect Vladimir Putin's return to the Kremlin.

Some 8,000 people participated in the March of Millions rally, which started from Kaluzhskaya Square before heading to Bolotnaya Square in downtown Moscow, Russian police was quoted as saying by the Itar-Tass news agency.

According to local media, protesters carried slogans such as " Full Power to People's Councils" in protest against Putin's governance. Some also called for social reform, including appeals for free healthcare.

Moscow police department said despite police warnings, organizers of the rally and some citizens stayed in the traffic area near the Udarnik cinema house, causing a stampede and injuries.

Later, opposition leaders Sergei Udaltsov, Boris Nemtsov and Alexei Navalny have been detained for provocation and the breach of public order during the March of Millions, the Itar-Tass said.

Also on Sunday, a pro-Putin rally was held in downtown Moscow to celebrate the first anniversary of All-Russia People's Front.

Russia has witnessed several massive rallies since parliamentary elections last December. Protesters accused Putin's United Russia party of voting fraud and demanded political reforms.

Putin, the most influential political figure in Russia, had already served two terms of presidency from 2000 to 2008.

On May 7, the incumbent prime minister will be inaugurated as the new Russian president for the third time after his triumph in the presidential election in March.