US President Barack Obama has urged his successor Donald Trump to stand up to Russia if it deviates from US "values and international norms".
Speaking in Berlin, Obama said he hoped the US president-elect would "not simply take a realpolitik approach" to dealing with Russia.
He also warned against a cyber arms race, saying there was clear proof Russia had engaged in cyber attacks.
Obama was speaking after talks with the German Chancellor Angela Merkel.
The two close allies stressed the need for continued close co-operation between their countries, as well as between the US and EU as a whole.