Trump, Putin shake hands ahead of high-stakes meeting at G-20

— -- President Donald Trump and Russian President Vladimir Putin shook hands and exchanged greetings at the G-20 summit in Germany ahead of their high-stakes meeting later today, according to the Kremlin's press secretary.

An official German government Facebook page posted a video of the two leaders briefly meeting and shaking hands, with President Trump patting Putin on the back.

Trump's first bilateral meeting as president with the Russian leader will come later today. The two heads of state have held three phones calls. According to an administration official, Trump and Putin will be joined at the meeting by U.S. Secretary of State Rex Tillerson, Russian Foreign Minister Sergey Lavrov and two translators.

The White House has said no agenda has been set for the discussion, but topics that are likely to come up include Syria and Ukraine. What's unclear is if Trump will reprimand Russia for its alleged hacking in the 2016 U.S. election and European elections.

Yesterday, in a press conference on foreign soil, President Trump questioned the U.S. intelligence community's findings that Russia meddled in the 2016 election and insisted "nobody really knows."

Protesters clash with police at the G-20 summit in Germany

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Protesters set barricades on fire, July 7, 2017, in Hamburg, Germany.

Markus Scholz/AFP/Getty Images

"I think it was Russia, but I think it was probably other people and/or countries," Trump said as he took questions during the press conference in Poland.

Trump also was tough on former President Obama, saying his predecessor "choked" and "did nothing" when he found out in August 2016 about Russia's cyber operation to disrupt the 2016 election.

The meeting between Trump and Putin in Hamburg, Germany, today comes as back home in the U.S., Special Counsel Robert Mueller investigates Russian interference in the U.S. election and whether there was any collusion between Trump's campaign associates and Russia.

ABC News' Marcus Wilford and Alexander Mallin contributed to this report.