Obama hopes Trump will 'stand up' to Russia when needed

President Obama, as he continues his final oversees trip as head of the United States, sought to reassure world leaders of his successor — even as it is unclear what foreign policies president-elect Donald Trump will keep or gut.

Obama said he hopes that Trump will be able to stand up to Russia when needed.

"I've sought a constructive relationship with Russia," Obama told reporters during a joint press conference with German Chancellor Angela Merkel on Thursday. "But what I have also been is realistic in recognizing that there is some significant differences in how Russia views the world and how we view the world."

Obama said he hopes Trump "doesn't take a realpolitik approach" and cut deals with Russia on Ukraine or Syria, among other issues. During the presidential campaign cycle, Trump was laudatory of Russian President Vladimir Putin and vowed to work to better U.S.-Russian relations.

Putin and Trump spoke last week following the business mogul's presidential win.

See President Obama with German Chancellor Angela Merkel:

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"My hope," Obama said on Thursday, is that "the president elect is willing to stand up to Russia when they are deviating from international norms."

The Obama administration deeply opposes Russian support of Syrian President Bashar al-Assad's regime and previously said Moscow's actions were creating a regional "quagmire."

As he visits Greece, Germany and Peru this week, Obama has been sitting down with a number of world leaders to offer encouragement to the international community on such issues as implementation of the Paris climate change and Iran nuclear agreements. Publicly and privately, the president and members of the administration have advocated with Trump in favor of these agreements.

Related: Obama During Final Foreign Trip: 'I Still Don't Feel Responsible' for Trump

See more photos from President Barack Obama's last tour of Europe:

During the contentious presidential campaign season, Trump sharply criticized a number of international agreements and alliances advocated by Obama and called NATO "obsolete." On Thursday, Obama said he is now encouraged by Trump's commitment to NATO.

It would be very difficult for Trump to enact a full-scale stop on Obama-backed agreements on reducing climate change and limiting Iran's nuclear weapons program, since those international deals involve global partners.

Among foreign leaders, Merkel has been among Obama's closest allies.

"We chose to go to Germany for a number of reasons" Obama deputy national security adviser Ben Rhodes told reporters before the president headed abroad. "First, Angela Merkel, who has been, I'd say, the president's closest partner over the course of his entire presidency. She's been there the entire time. They've worked together on almost every issue. They've developed a deep mutual respect, I think, and close friendship as well. So he wanted to see Chancellor Merkel one more time to thank her for her partnership and leadership."

Related: Obama Races to Protect His Achievements From Trump

Amid the refugee crisis caused largely by the Syrian civil war, Merkel has joined the American president in being a forceful advocate in urging other nations to take in those fleeing violence and unrest in their home countries. Like Obama, she has also tried to stop the rising tide of nationalism and anti-globalization that helped lead to the growing influence of far-right parties across Europe and Trump's election in the U.S.

Obama said he is "cautiously optimistic" that the gravity of holding the Oval Office will weigh on Trump and that it will help guide his decisions.

See iconic photos of Obama: