"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," Putin said, his right hand placed on a red-bound copy of the Russian Constitution as he officially took over reins from Dimitry Medvedev.
In a brief but glittering ceremony, Putin, 59, hailed a "reborn" Russia and promised a new stage in its development.
Putin, who was president of the former Soviet republic from 2000-2008, returned to claim the presidency after an absence of four years in which he served as prime minister.
Putin was forced to step down in 2008 by a Constitutional clause that forbids more than two subsequent terms, but is silent on further presidential stints. He then shifted to the post of prime minister after installing his protege Medvedev in the Kremlin, but remained by far Russia's most powerful politician.
Putin, a former KGB officer, won a third term as president in controversial elections in March which were marked by allegations of vote rigging in favour of his United Russia party.
The chorus of anti-Putin voices has increased in recent months, with several protests erupting out against his domination of the Russian polity for 12 years -- first as president and then as prime minister.
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Yesterday, thousands of protesters opposed to the inauguration clashed with police in Moscow. Prominent opposition activists Alexei Navalny, Sergei Udaltsov and Boris Nemtsov were among dozens detained.
If he completes his six-year term, Putin will be the longest serving Russian leader since Joseph Stalin.