Faced with an expected influx of around one million refugees this year alone, Germany is looking to its EU partners to help manage the crisis but is running up against resistance from some countries, particularly in eastern Europe.
"Either Europe stands together and acts with solidarity in times of hardship for hundreds of thousands, or fences and barriers will again be raised," Steinmeier said in a speech to fellow Social Democrats (SPD) at their annual party congress, Reuters reported.
"And then the vision of a united Europe crumbles," added Steinmeier, a former leader of the Social Democrats, who are the junior partner in Germany's coalition government with Chancellor Angela Merkel's conservatives.
He called for boldness to push ahead with the European project and "to oppose the right-wing populists."