MOSCOW (NYTIMES, REUTERS, AFP) - Vladimir Putin took the oath of office Monday (May 7) for a fourth term as Russia's president, in a ceremony staged in a gilded Kremlin hall and replete with pageantry that highlighted his vast accumulation of authority after nearly two decades in power.

Putin, a former KGB agent, has ruled Russia as prime minister or president for more than 18 years, and in that time has crafted an image as a steely nerved leader and the man best qualified to rebuild his country after the collapse of the Soviet Union.

In a theatrical touch, a televised ceremony began Monday with Putin sitting at his desk in the Kremlin, suit jacket looped over his chair, as if hard at work until moments before the ceremony. A phone rang, letting him know it was time for his fourth term; he donned his jacked and walked alone through the red-carpeted Kremlin corridors and into a hall packed with about 6,000 invited, cheering guests.

Standing in the Grand Kremlin Palace's ornately-decorated Andreyevsky Hall with his hand on a gold-embossed copy of the constitution, Putin swore to serve the Russian people, safeguard their rights and freedoms, and defend Russian sovereignty.

In a short speech, Putin suggested his focus had now turned to domestic matters and improving Russia's economy for the "well-being of every family," though there were no words of reconciliation in the country's tense relations with the West.

Putin, 65, won re-election in March after 77 per cent of voters backed him in a presidential election, the largest margin for any post-Soviet leader. It was a result his backers said showed widespread support, but one his critics dismissed as illustrating the stifling of any real opposition.

US President Donald Trump on Monday congratulated Putin on being sworn in for his fourth term, the White House said, while highlighting the importance of freedom of assembly, after the mass arrest of protesters.

"The president congratulates him and looks forward to a time when we can hopefully have a good relationship with Russia," White House Press Secretary Sarah Sanders told reporters.

"However, the United States believes that everyone has a right to be heard and assemble peacefully."

On Saturday, nearly 1,600 protesters including Putin's most vocal opponent, Alexei Navalny, were detained during nationwide rallies against the Russian leader under the slogan "Not Our Tsar."

Abroad, Putin has sought to restore Russia's sway in world affairs. During his third term as president, he intervened militarily in Ukraine and Syria, putting him at loggerheads with the West. And, according to US intelligence agencies, he directed Russia to meddle in the 2016 presidential election to aid Donald Trump.

At home, he has presided over the restitution to power of the security agency he once served, with many high officials and corporate executives now former officers like Putin.

But the domestic economy has continued to lag, only recently emerging from a painful recession. He has also clamped down on critics, arresting scores of opposition activists and restricting the media.

MEDVEDEV STAYS

In his first act after being sworn in, Putin stuck with his long-serving prime minister Dmitry Medvedev, signalling that he would keep faith with a policy direction that has brought Russia into conflict with the West.

Some Kremlin-watchers had speculated Putin might bring in a fresh face as prime minister to kick-start reforms of the sluggish economy and revive foreign investment curtailed by stand-offs with the West.

By choosing Medvedev - seen by people close to the Russian elite as a safe pair of hands whose chief quality is loyalty to his boss -
Putin indicated he favoured continuity.

The choice is also likely to be parsed by Kremlin-watchers for any clues about what happens after Putin's current term ends in 2024. The constitution bars him from seeking a third consecutive term.

When Putin came up against the same term limits in 2008, he got around the problem by anointing Medvedev as president, before taking back the job after one term. Some observers believe Putin, who has not anointed any heir apparent, could attempt the same manoeuvre a second time.

RUSSIAN-MADE LIMOUSINE

Putin has switched to travelling in a new Russian-made limousine, ditching the imported vehicles he has been using up to now, Russian state television reported on Monday.

The new Russian limousine had its first public outing on Monday when Putin climbed into the vehicle to travel the short distance from his office to the Kremlin hall where he was to be sworn in for another term in office.

Details of the new limousine have not been revealed, but it will become the heir to the Russian-made ZIL sedans that for decades transported Soviet leaders.

Putin has said that Russia should reduce its dependence on imported goods and technology, a drive that has gathered pace since Russia was hit by Western sanctions.