"That is a major threat and provocation. North Korea should stop immediately and that's why we will examine possibilities of ramping up sanctions," said Moon in Berlin before talks with German Chancellor Angela Merkel.
"At the G20 summit, we will discuss this with various government representatives," he said, two days before the gathering of world leaders in the port city of Hamburg.
Moon is due to meet with Japanese Prime Minister Shinzo Abe and US President Donald Trump tomorrow evening.
"This is a concern that lies close to our hearts because we know from our own experience what a divided country means, and how happy we were when we were able to restore German unity in 1989," said Merkel.
The pro-Western and pro-Soviet states of West and East Germany reunified after the fall of the Berlin Wall in 1989, becoming one of the most stable and prosperous democracies in the world.