SOFIA, Nov. 27 (Xinhua) -- Bulgarian President Rumen Radev and his Polish counterpart Andrzej Duda here on Tuesday called for the de-escalation of Russia-Ukraine tensions.

According to Radev, in this situation the two sides needed to show restraint and the fastest possible de-escalation through dialogues, without the use of force.

"For us as neighboring countries in this region it is extremely important to prevent further escalation of tension," Radev said.

Duda also said that there was no doubt that the return to a condition of de-escalation of tension in the Sea of Azov was needed.

This situation was unacceptable, and he hoped the tension would be de-escalated in the near future, Duda said.

On Sunday, the Ukrainian Navy said that Russian forces opened fire and seized three Ukrainian ships near the Kerch Strait, which separates the Black Sea and the Sea of Azov, injuring six Ukrainian military sailors.

Russia's Federal Security Service said that the Ukrainian ships breached the Russian border, and conducted dangerous maneuvers in spite of Russia's orders.

Relations between Russia and Ukraine have been deteriorating since Crimea was incorporated into Russia in March 2014 following a local referendum that was rejected by Kiev and Western countries.