The Azov seabed is reputedly rich in oil reserves, while the Kerch Strait, which permits access to the Black Sea, is of strategic military importance.
Last year, Russian authorities unilaterally started building a dam across the Kerch Strait toward the tiny Ukrainian island of Tuzla. Ukraine warned it would not allow construction to proceed to its side of the waterway and implied it would use force by posting soldiers on Tuzla.
The work was halted after both sides agreed to negotiations.
Ukraine has long wanted an international line in the sea to define who owns what.
Yesterday's agreement gives Russia what it wanted. It fixes the legal status of the Sea of Azov and the Kerch Strait as inland waters of the two countries. It provides for joint use of the Azov-Kerch water area and bans the entry of warships of third countries without mutual consent. That will prevent Ukraine from inviting NATO warships to joint maneuvers in the Sea of Azov, something it has never done but a possibility Russia wanted to sink.
Russian Foreign Minister Sergei Lavrov said a detailed resolution of the Tuzla dam issue is still in the works, but he assured the Russian State Duma that all of Russia's interests will be taken into account.
The two parliaments also ratified an agreement on the Russian-Ukrainian state border, which was signed by the presidents of both countries in January 2003. It concerns regulations for border crossings by private individuals and commercial entities and stipulates the permanency of the border.
The third treaty ratified yesterday is an agreement for a Single Economic Space (SES), which envisages a common tax code, customs union, foreign-trade policy, and joint financial policies, possibly leading to a common currency.
Lavrov said the ratifications meet the goal of strengthening the "strategic partnership" between Russia and Ukraine. However, he said Moscow is dissatisfied with some aspects of its relations with Kyiv, particularly its desire to join NATO.
"Clearly, not everything in Russian-Ukrainian relations is satisfactory to us. We have taken note of the recent growth of the so-called Euro-Atlantic vector in Ukraine's foreign policy and the increased level of its cooperation with NATO," Lavrov said. "There are still problems with the humanitarian rights of our fellow countrymen [in Ukraine]. Nevertheless, we are convinced that the development of a strategic partnership between our countries must be active, and not passive."
The human rights concern refers to Ukraine's announcement last week that all of the country's national radio and television channels must broadcast in Ukrainian, with other languages being used only in areas with a significant ethnic minority.
The ruling has angered many of the millions of ethnic Russians who live in Ukraine.
Ukrainian Foreign Minister Kostyantyn Hryshchenko said the three agreements "meet the country's national interests." Referring to the Azov and Kerch accord, he said Ukraine and Russia will use the sea jointly but that each country will have its own zone of responsibility.
Opponents say the agreements threaten Ukraine's sovereignty.
Referring to the Azov and Kerch agreement, a member of parliament from the opposition party Our Ukraine, Oleh Tyahnebok, says deputies were not provided with information before the vote explaining where the borders ran.
"As to the agreement between Ukraine and Russia about the border, I didn't want members of parliament to be blind kittens, but they voted without maps or definitions of the national borders," Tyahnebok said. "We didn't see where this border between Ukraine and Russia was. This is a threat because Russia, which was always greedy for territory as far as Ukraine went, can according to its documents grab half of Ukraine."
The Ukrainian parliament stipulated the agreements must not contradict the country's constitution.