Russia is in need of vast improvements, Vladimir Putin has said as he was inaugurated for his fourth term as president, approaching two decades in power.

“The purpose of my life and my work is to serve the people and our fatherland. This is what is most important for me,” Mr Putin said in a speech after taking the oath in the Kremlin on Monday in front of about 5000 guests.

Former German chancellor Gerhard Schroeder, who last year became board chairman of Russian state oil giant Rosneft, stood in the front row between Russian Prime Minister Dmitry Medvedev and the Russian Orthodox Church’s Patriarch Kirill.

Russia is in need of improvement in many areas to ensure a free and just society, Mr Putin said, adding that the world is rapidly changing and Russia needs to keep up.

The 65-year-old has already been in power for 18 years. He side-stepped a constitutional ban on serving more than two consecutive presidential terms by serving as Prime Minister between 2004 and 2008.

The country, which still needs to overcome setbacks incurred during the turbulent 1990s, “should be modern and dynamic,” Mr Putin said, adding that health care and other social services must improve.

“We need breakthroughs in all spheres,” he said.

Russia has repeatedly overcome harsh periods in its 1000-year history, he said.

“We are a single powerful team capable of overcoming any obstacle.”

Having cultivated a reputation as the guarantor of Russia’s stability, Mr Putin won re-election in March with more than three-quarters of the votes, or 76 per cent.

The Organisation for Security and Cooperation in Europe (OSCE), which independently monitored the election, said there was a “lack of genuine competition.”

Domestic media coverage was overwhelmingly in favour of the incumbent, and voters were unduly pressured to cast their ballots to increase turnout, the OSCE said.

Mr Putin was inaugurated for his fourth term as President. Photo: AP

On the weekend before Mr Putin was sworn in, a fierce challenger, opposition leader Alexei Navalny, and about 1600 of his supporters were detained as protests were held across the country.

Mr Navalny was barred from running in the election over a financial crimes conviction that he says was trumped up. No other candidate was a serious challenge to Mr Putin. The runner-up, from the Communist Party, received about a 10th of the votes.

Following protocol, Mr Medvedev and his cabinet left office on Monday after the president was sworn in.

Mr Putin is expected to reappoint Mr Medvedev, and the Russian parliament has already called a special sitting for Tuesday to vote on the appointment.

After this six-year term, Mr Putin will be next eligible to run for president in 2030, at age 77, unless the constitution is changed.

The United Russia party, which staunchly supports Mr Putin, controls enough seats in parliament that it could unilaterally amend the constitution.