Ambassador-at-large Valery Kenyaikin, speaking after the 25th round of talks between the countries' delegations on the issue, said: "Means for demarcating the territories turned out to be inconsistent," in reference to a draft agreement on the Azov border.
Russia remains committed to the Kerch agreement signed in 2003 by Russian President Vladimir Putin and his then Ukrainian counterpart Leonid Kuchma.
"All agreements on this issue should follow from this agreement, and not consist of reviewing the document," Kenyaikin said.
The diplomat said Ukraine had proposed changing the status of the Azov Sea, from territorial to international waters.
On the Kerch Strait issue, Kenyaikin said the sides had "acknowledged differences in opinion over the practical implementation of the precepts of international law."
During talks, the sides manage to make progress on the issue of demarcating the Black Sea, he said, adding that the Russian negotiators had submitted a draft agreement.
The confrontation over the Tuzla Island in the Kerch Strait erupted in summer 2003 when Russia's attempt to construct a dam there provoked a bitter dispute with its neighbor, which accused Russia of encroaching on its territory.
