Chancellor Angela Merkel called for the release of Ukrainian seamen from Russian President Vladimir Putin. That's what she told Putin in a telephone conversation, government spokesman Steffen Seibert said.
Two weeks ago, the Russian Coast Guard had denied three Ukrainian ships passage through Kerch Strait, arrested the ships and arrested 24 crew members.
The strait in front of the Russian-occupied Crimea peninsula connects Black with the Sea of Azov and is considered by Moscow to be the sole Russian territory. The incident has triggered significant tensions between Moscow and Kiev.
Merkel underlined in the conversation with Putin that precautions were necessary to ensure a smooth ship passage, Seibert said.
On Tuesday, the foreign policy advisors of the heads of state and government of Germany, France, Russia and Ukraine will meet in Berlin. Merkel had announced the attempt to mediate after her meeting with Putin at the G20 summit in Buenos Aires.