"We are entering a new stage of national development. We want to live in a democratic country … in a successful Russia," Putin said.
"I consider it to be my life's meaning and duty to serve my fatherland and our people."
Police arrested 120 of 200 protesters who demonstrated Monday against Putin's return to the presidency, RIA Novosti reported.
Putin, with his right hand on the Russian Constitution, took the oath of office, saying, "I swear on the power invested in my as president of the Russian Federation to respect and protect the rights and freedom of its citizens."
This six-year term is Putin's third term as president. He was president for two consecutive four-year terms from 2000 to 2008. From 2008 until last year, Putin was prime minister under Dmitry Medvedev's regime.
Russia's constitution was amended to expand the presidential term to six years.
Putin's motorcade moved through empty streets locked down by a heavy security presence en route to the Kremlin State Palace, where 2,000 guests, including former Italian Prime Minister Silvio Berlusconi, gathered to witness his inauguration, RIA Novosti said. Patriarch Kirill, leader of Russia's Orthodox Church, blessed Putin's inauguration during a service at the Kremlin.
On Sunday, the most violent demonstration yet against Putin's return to the presidency injured dozens of people, police and witnesses said.
Protesters pelted riot police with bottles, rocks, asphalt chunks and flares after police, standing four rows deep, blocked the demonstrators' path during a government-sanctioned procession to Bolotnaya Square near the Kremlin, witnesses said.
The police responded with a crushing use of force, "clubbing demonstrators" who broke through police lines, RIA Novosti Britain's Guardian newspaper reported people were dragged -- sometimes by their hair -- to awaiting arrest vans. Police also fired pepper spray into the crowd, witnesses said.
Dozens of people were injured, including 20 police officers, authorities said.
A photographer died after falling six stories from a fire escape while filming the protest, ITAR-Tass reported.
More than 450 people were arrested, including anti-corruption activist Alexey Navalny, leftist activist Sergei Udaltsov and former Deputy Prime Minister Boris Nemtsov, police said.
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