Ahead of a formal, sit-down meeting, Trump and Putin were seen exchanging pleasantries as a leaders’ retreat got under way in Hamburg. As officials gathered around a table, Trump outstretched his hand to Putin and then patted his elbow and both men smiled. A brief video clip shows Trump casually patting Putin on the back as they stand side by side.

Video of the brief exchange was posted to Facebook by the German Cabinet. It was the first known in-person interaction between the two men, who have spoken by telephone since Trump was inaugurated in January.

The two leaders planned later Friday to hold longer talks on Syria and other issues on the sidelines of the Group of 20 summit of industrialized and developing nations. The White House said it has scheduled 35 minutes for the meeting.

“Much to discuss,” Trump tweeted in advance of the encounter.

In this image taken from video U.S. President Donald Trump, centre left, meets with the Russian President Vladimir Putin, centre right, during the G20 summit in Hamburg, Germany Friday July 7, 2017. (Steffen Kugler/German Government via AP)

The heavily anticipated meeting is being closely scrutinized for signs of how friendly a rapport Trump and Putin will have. Trump’s predecessor, President Barack Obama, had notoriously strained ties to Putin, and Trump has expressed an interest in a better U.S.-Russia relationship. But deep skepticism about Russia in the U.S. and ongoing investigations into whether Trump’s campaign coordinated with Moscow during last year’s election have made a U.S.-Russia detente politically risky for Trump.

As leaders gathered at a summit hall in Hamburg for a group photo, Trump and Putin stood on opposite sides of the tableau. Putin chatted casually with German Chancellor Angela Merkel before taking his spot for the photo next to Turkish President Recep Tayyip Erdogan. After the cameras snapped away, Merkel, in the center, dismissed the group with a firm nod of the head.

In the lead-up to the meeting, Trump, during a speech in Warsaw on Thursday, urged Russia to “cease its destabilizing activities in Ukraine and elsewhere and its support for hostile regimes — including Syria and Iran — and to instead join the community of responsible nations in our fight against common enemies and in defense of civilization itself.”

But much of the focus — both in Washington and Moscow — will be on whether Trump broaches the issue of Russia’s meddling in the election.

During a news conference in Poland on Thursday, Trump again refused to accept the conclusion by multiple U.S. intelligence agencies that Russia interfered to try to help Trump win last November. Trump said it could have been Russia, but that other countries could have meddled, too.

In this image taken from video U.S. President Donald Trump, left, shakes hand with the Russian President Vladimir Putin during the G20 summit in Hamburg Germany, Friday July 7, 2017. (Steffen Kugler/German Government via AP)

“Nobody really knows for sure,” Trump said.

U.S. lawmakers and federal investigators continue to look into Russia’s election interference, along with possible collusion between Trump campaign associates and Russian government officials. That puts Trump under intense scrutiny over how he handles the sit-down with Putin, a former Russian intelligence agent known to come to meetings like this well-prepared.

Trump, who likes to have neatly packaged achievements to pair with high-profile meetings, may seek some concessions from Russia to show he’s delivering progress and helping restore a once-productive relationship that he recently described as being at an “all-time low.” Putin would almost certainly want something in return.

The list of issues ranges from Syria to Iran to Ukraine, and now North Korea, following Pyongyang’s test this week of a missile capable of striking the U.S.

Russia wants the U.S. to return the two compounds in New York and Maryland that were seized by the Obama administration as punishment for election meddling. It also wants the U.S. to ease sanctions it imposed on Russia after Putin annexed the Crimean Peninsula, and over Russia’s support of separatist elements in Ukraine.

The U.S. wants a resumption of adoptions of Russian children by American parents, which Russia banned in 2012, along with an end to what it claims is intensifying harassment of U.S. diplomats and other officials stationed in Russia.