US President Barack Obama has called on his successor Donald Trump to stand up to Russia, underscoring a major concern that overshadowed his meeting with German Chancellor Angela Merkel.

Following their meeting in Berlin on Thursday, Obama and Merkel held a press briefing to address the future of relations between the US and Europe under the pending presidency of Trump.

Referring to Trump’s many indications at “normalizing” ties with Russia, Obama said he hoped that the New York businessman would protect American values and avoid taking a “realpolitik” approach in his dealings with Moscow.

“I've sought a constructive relationship with Russia but what I have also been is realistic in recognizing there is some significant differences in how Russia views the world and how we view the world,” the outgoing president said.

“And my hope is the president-elect coming in takes a similarly constructive approach: Finding areas where we can cooperate with Russia, where our values and interests align” and at the same time be “willing to stand up to Russia where they are deviating from our values and international norms,” Obama added.

US President-elect Donald J. Trump (Photo by AFP)

During his time in the White House, Obama tried to unite Europe against what he referred to as the “Russian aggression,” using NATO and economic means to put pressure on Moscow.

Trump’s willingness to cooperate with Russia and review Washington’s ties with NATO, however, has stirred concerns among America’s European allies, who have been at loggerheads with Moscow over various issues such as Western sanctions against Russia, the Ukraine conflict and Russia's involvement in Syria.

“I don't expect that the president-elect will follow exactly our approach, but my hope is he does not simply take a realpolitik approach and suggest that, you know, if we just cut some deals with Russia, even if it hurts people or even if it violates international norms or even if it leaves smaller countries vulnerable, or creates long-term problems in regions like Syria, that we just do whatever's convenient at the time,” Obama said at the press conference.

US President Barack Obama waves as he and German Chancellor Angela Merkel leave after addressing a press conference at the chancellery in Berlin, November 17, 2016. (Photo by AFP)

He also hailed Merkel as an “outstanding” international partner who understands “that part of good leadership on behalf of the nation requires engaging the world as a whole.”

Prior to their meeting, Obama and Merkel issued a joint op-ed in the German daily Wirtschaftswoche, maintaining that Germany and the US would retain their close relations and remain committed to the NATO military alliance under Trump.

Obama’s trip to Germany was part of his last official overseas trip. Prior to visiting Germany, Obama flew into the Greek capital of Athens on Tuesday to hold talks with President Prokopis Pavlopoulos and Prime Minister Alexis Tsipras.

He will conclude his tour with a stop in the South American nation of Peru for a summit of the Asia-Pacific Economic Cooperation forum (APEC).