"Turkey remains a key to [solving] the migration problem in Europe. We need Turkey, if we want to seriously reduce the flow of refugees to Europe this year," Frank-Walter Steinmeier pointed out.
His remarks came a few months after the European Commission set up a 3 billion euro (more than $3.2 billion) fund for Turkey to help it boost border security and accommodate about 2.2 million Syrian refugees.
Currently, Turkey hosts over 2.2 million Syrian asylum seekers as well as around 230,000 desperate migrants from other countries, more than any other country hosting foreign refugees.
Meanwhile, Greece's President Prokopis Pavlopoulos has blamed Turkish border authorities of facilitating people smuggling by turning a blind eye to the trafficking of thousands of migrants to Europe.
"I have a strong fear that Turkish smugglers have the support of the authorities, in particular, border authorities who act like they have seen nothing," he said in an interview with the German newspaper Sueddeutsche Zeitung.
The European Commission said, in turn, that the current migration crisis is the biggest such deadlock since the Second World War.