BERLIN - German Foreign Minister Heiko Maas said on Monday that the recent Kerch Strait incident, during which three Ukrainian ships illegally crossed Russian territorial waters, was still causing concerns.

"The situation around the Sea of Azov is still causing concerns. This is great that navigation via the Kerch Strait has been renewed, and it should be maintained in the long-term perspective.

But while there are prisoners — and these are the Ukrainian sailors — the conflict is not resolved and can trigger further escalation," Maas said upon his arrival at the EU foreign ministers' meeting in Brussels.

Maas went on to say that Germany expected both Russia and Ukraine to make steps toward de-escalation, also pointing out that the EU foreign ministers were going to discuss how the European Union could contribute to the conflict settlement.

On November 25, three ships of the Ukrainian Navy — Berdyansk, Nikopol, and Yany Kapu — breached the Russian border, entered Russian territorial waters that were temporarily closed, and began moving toward the Kerch Strait, which serves as an entrance into the Sea of Azov.

Moscow has refuted Kiev's claims that Ukrainian sailors, detained after failing to respond to a lawful demand to stop, were prisoners of war. They faced criminal charges over state border breach.