Russian President Vladimir Putin on Thursday dropped a cryptic hint seen by some as a sign he may not serve another term while also staunchly defending his Kremlin policies in a marathon news conference.

Clocking in at four hours and twenty-five minutes, the question-and-answer session was one of the longest ever held by Putin in a format that has become an annual end-of-year tradition for the Russian leader.

Putin -- who will shortly mark two decades since Boris Yeltsin dramatically handed him the presidency at the start of 2000 -- faced the media with Russia still isolated internationally and speculation growing about his own plans when his mandate ends in 2024.

Many of the questions posed by some 1,800 reporters accredited for the event focused on bread-and-butter regional issues in a country that stretches from the Baltic to the Pacific, which Putin traditionally responded to with a stream of statistics.

But the most talked about moment came when Putin indicated he was in favour of removing the word "successive" from a clause in the constitution that says the Russian president should only serve two successive terms.

Were this to be implemented, Putin could not when his current term runs out in 2024 repeat the trick of 2008 where he temporarily handed the Kremlin to his ally Dmitry Medvedev to get round the two mandate rule.

"Your humble servant served two successive terms and then stepped down and had the constitutional right to return to the post of president," he said.

"But some of our political scientists and activists do not like this and maybe this could be removed, possibly."

Margarita Simonyan, the well-connected editor-in-chief of Russian broadcaster RT, said on Twitter: "If anyone had any doubts about whether the chief will seek another presidential term, he will not."

But with no successor in sight at this stage, Tatiana Stanovaya, head of the R.Politik analysis firm, said it was not clear if Putin's comments represented an "incentive to start a discussion or a decision that will be realised".

Russian President Vladimir Putin is seen on a large screen as he speaks during his annual press conference in Moscow
Russian President Vladimir Putin is seen on a large screen as he speaks during his annual press conference in Moscow AFP / Alexander NEMENOV

"He has increased the arguments in favour of a scenario of stepping down. Now the search for a successor will begin," she told AFP.

But asked to sum up his two decades in office -- which saw him named premier by Yeltsin in 1999, serve as president from 2000-2008, again premier from 2008-2012 and then return as president -- Putin said Russia in 2000 and 2019 were "two different countries".

He said Russia had been in the throes of "civil war" with the conflict in Chechnya when he took office while the economy had also "totally transformed" since the 1998 financial crisis.

Although Putin's popularity ratings have weakened since the peak of the boost from the 2014 annexation of the Ukrainian peninsula of Crimea, he still retains the support of a majority of Russians.

However, those watching on YouTube made clear they were unimpressed, with 43,000 pressing dislike and just 10,000 likes and some posting mocking comments.

In other crucial comments in the press conference:

-- Putin said the impeachment of Donald Trump was based on "made-up" grounds and he did not believe that the US president was in any way finished.

-- He said "nobody knows" the true causes of climate change, indicating that global warming could be caused by astronomical factors like a tilt in the Earth's axis rather than man-made factors.

-- The body of Bolshevik leader Vladimir Lenin should stay in its mausoleum on Red Square in Moscow, Putin said, while admitting he had changed his mind from his KGB days and now had a less rosy assessment of him.

-- He denied Russian military forces had any involvement in the breakaway Ukrainian regions of Donetsk and Lugansk and said mercenaries in the conflict included Germans and French on both sides.

As in previous editions, dozens of journalists clamoured at Putin to be allowed to ask questions, bearing placards with the names of their media, home regions or simply expressions of admiration for the Russian leader.

The length was not far off the record for Putin's now notorious press marathons, four hours forty minutes in 2008.

But in an unexpected question at the end, a Russian journalist asked Putin about the successful business activities of his two daughters whom he never discusses in public. Visibly irritated, he did not directly answer the question.