German Chancellor Angela Merkel has urged "freedom of shipping into the Sea of Azov" in a private talk with Russian President Vladimir Putin on the sidelines of the Group of 20 summit in Buenos Aires.
Merkel's spokesman, Steffan Seibert, said the December 1 talks focused on the conflict in Syria and tensions between Russia and Ukraine.
On November 25, Russia seized three Ukrainian naval vessels and 24 Ukrainian sailors near the Kerch Strait as they were seeking to enter the Sea of Azov. Russia has charged the seamen with illegally crossing the country's border.
The European Union and the United States have criticized Russia's action and have called for the immediate release of the ships and crews.
France and Germany have offered to mediate between Russia and Ukraine.
Merkel and Putin agreed that the four countries should hold additional talks at the "adviser level," Seibert said.
Kremlin spokesman Dmitry Peskov said that Merkel asked Putin to release the Ukrainians, but Putin said that was a matter for the courts.
Peskov said Putin provided Merkel with a "detailed" explanation of the Kerch Strait incident.
Peskov also said that "mediation" was not discussed and most likely would not be possible.
Peskov confirmed that Putin spoke briefly with U.S. President Donald Trump, but did not elaborate.
Earlier, Russian presidential aide Yury Ushakov said Putin expressed his "regret" that he and Trump were unable "to talk properly" at the G20 summit.
Ushakov added that the two sides agreed to maintain contacts, including dialogue through U.S. national-security adviser John Bolton.
In an interview with CNN, U.S. Secretary of State Mike Pompeo said Trump cancelled a planned meeting with Putin "to send a clear, unambiguous message" that the United States believes Russia's conduct in the incident was "deeply inconsistent with international law."
Relations between Russia and the West have been severely strained since Moscow's 2014 annexation of the Ukrainian Black Sea region of Crimea and over Russia's military, political, and economic support for separatist movements in parts of eastern Ukraine.
More than 10,300 people have been killed in the conflict in eastern Ukraine since April 2014.