US President Barack Obama and European leaders have stressed that NATO members must maintain their military alliance and vowed to continue sanctions against Russia over its alleged involvement in the Ukraine conflict.

NATO members also agreed that the only way to end the Syrian conflict is with a diplomatic solution. The statements were made as European nations openly question how Donald Trump's leadership could affect transatlantic ties.

President Obama was in Germany on Friday, in a bid to reassure European partners that the US values good transatlantic relations.