“Such a decision, which was made at the beginning of 2022, should have been made earlier," he told his annual press conference in Moscow.

"The events in Crimea were spontaneous, and the events of 2022 were also started without any special preparation. Why did we start? Because it was no longer possible to stand still and endure, waiting for the situation to worsen for us.”

Putin says Russia has no preconditions to start talks with Ukraine on a possible peace settlement.

Putin said that a preliminary agreement reached between Russian and Ukrainian negotiators during the early weeks of the war at talks in Istanbul, which was never implemented, could serve as a basis for future discussions.

Putin said that the current situation on the battlefield should also be taken into account in any talks, while fielding questions on state TV during his annual marathon question-and-answer session.

Ukrainian President Volodymyr Zelenskiy said there were no Istanbul agreements between Ukraine and Russia during a press conference at the European Council meeting in Brussels.

"Ukraine did not agree to the ultimatum from the Russian Federation," Zelenskiy said.

"Ukraine did not sign anything, no agreements existed. There was a response to the ultimatum from the Russian Federation."

If and when a deal was reached, Russia would be ready to sign it only with the legitimate authorities of Ukraine, which for now the Kremlin considered to be the Ukrainian parliament, Putin said on Thursday.

Russia was ready to conduct negotiations with Zelenskiy, Putin said but added that the Ukrainian president - whose term has technically expired but who has delayed an election because of the war -would need to be re-elected for the Kremlin to consider him a legitimate signatory to any deal to ensure it was legally watertight.

Putin dismissed the idea of agreeing a temporary truce with Ukraine, saying only a long-lasting peace deal with the country would suffice.

Putin also said he was ready to compromise over Ukraine in possible talks with US president-elect Donald Trump on ending the war.