Ivanov said the agreement covering Russia's use of the naval base it uses in Crimea is part of a broader Russian-Ukrainian border treaty.
He said that changes to the lease would "seem fatal."
Ukraine is currently in a dispute over gas prices with Russia's state-run gas firm. Ukrainian officials have suggested charging higher prices for use of the naval base to offset the increase Moscow wants to charge Kyiv for the price of gas.
Ukrainian Prime Minister Yuriy Yekhanurov today said that Ukraine has the "unquestionable" legal right to take 15 percent of Russian gas shipments passing through its territory as a transit fee.
(AP/Reuters/AFP)