The Estonian Foreign Ministry summoned Russian envoy Alexander Petrov on Wednesday following a clash between Moscow and Kiev in the Kerch Strait.
"At a meeting with the ambassador, the Foreign Ministry called on Russia to immediately release the ships and their crew members," the ministry said.
The statement comes just days after Ukrainian ships crossed the Russian maritime border and moved from the Black Sea towards the Kerch Strait. Russian Border Guard seized the ships after they not react to demands of the vessels escorting them and made dangerous manoeuvers, the Federal Security Service (FSB).