Trump says Russia abandoned Syria's Assad, never should have been involved

US President-elect Donald Trump said on Sunday that Russia's abandonment of Syrian President Bashar al-Assad led to his downfall, adding Moscow never should have protected him in the first place and then lost interest because of a war in Ukraine that never should have started.

"Assad is gone. He has fled his country. His protector, Russia, Russia, Russia, led by (President) Vladimir Putin, was not interested in protecting him any longer," Trump wrote on his social media platform Truth Social.

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"There was no reason for Russia to be there in the first place," Trump wrote. "They lost all interest in Syria because of Ukraine ... a war that should never have started, and could go on forever."

Trump, who takes office on Jan. 20, added that Russia and Iran, Assad's other main backer, "are in a weakened state right now, one because of Ukraine and a bad economy, the other because of Israel and its fighting success".

Trump, who has said he will seek to halt the Ukraine war rapidly, met Ukraine's President Volodymyr Zelenskiy on Saturday in Paris where they were both attending a ceremony to reopen Notre-Dame Cathedral.

He said Russia and Ukraine had both suffered hundreds of thousands of dead and wounded troops, and Ukraine had also lost many civilians. He added the Ukrainian leader "would like to make a deal and stop the madness ... There should be an immediate ceasefire and negotiations should begin".

"I know Vladimir well. This is his time to act. China can help. The World is waiting!"