Vladimir Putin took the oath as Russia's president Monday with a ringing appeal for unity at the start of a six-year term in which he faces growing dissent, economic problems and bitter political rivalries. Soon after his swearing-in, Putin proposed his Kremlin predecessor Dmitry Medvedev as the country's new prime minister under a job swap agreement that sparked protests last year. Outside the Kremlin's high red walls, riot police prevented protests by rounding up 120 people, including men and women in cafes wearing the white ribbons symbolizing opposition to Putin, a day after detaining more than 400 people during clashes. But in the Kremlin, 2,000 dignitaries applauded Putin's every step down the red carpet into a vast hall with gilded columns, the throne room of the tsars, where he was sworn in with his right hand resting on the red-bound Russian constitution. “We will achieve our goals if we are a single, united people, if we hold our fatherland dear, strengthen Russian democracy, constitutional rights and freedoms,” Putin said in a five-minute speech after taking the oath for the third time. “I will do all I can to justify the faith of millions of our citizens. I consider it to be the meaning of my whole life and my obligation to serve my fatherland and our people.” Although he has remained a dominant leader for the past four years as prime minister, Putin, 59, has now taken back the formal reins of power he ceded to Medvedev in 2008 after eight years as president. Parliament is expected to approve Medvedev, 46, as prime minister Tuesday, completing a job swap that has left many Russians feeling disenfranchised two decades after the Soviet Union collapsed.