"If we fail to agree with Russia [on maritime border demarcation] at a bilateral level, we could apply the international law of the sea," Ukraine's UNIAN news agency quoted Oleksandr Kupchyshyn as saying.
The two countries have been in a dispute over their maritime borders since the early 1990s. Ukraine insists that a border be drawn in the Kerch Strait, which links the Sea of Azov to the Black Sea, that matches the administrative border that existed between Russia and Ukraine in the former Soviet Union.
Russia maintains that inland water areas were not subject to borders in the Soviet era, and therefore this principle is not applicable.
Ukraine's Foreign Ministry has said the two countries failed to make progress in border demarcation talks held in Kiev on January 21-22.