Relations between Russia and NATO have improved dramatically over the past 15 years, and the present situation is totally different from what it was then, said Deputy Assistant Secretary for European and Eurasian Affairs Steven Pifer.

The main conditions for Ukraine one day succeeding in its bid to join NATO were economic and military reforms, as well as democratic progress, Pifer added.

If those conditions were met, there was a real possibility for Kiev to join the alliance, he said.

Ukraine's defense minister Evhen Marchuk said Tuesday that Kiev would not review an agreement with Moscow allowing Russia's Black Sea fleet to be based in Ukrainian territory until 2017.

"The question of the Russian fleet in Crimea and Ukraine's strategy of cooperation with the Atlantic alliance, with the aim of eventually becoming a member, are not mutually exclusive," Marchuk said.

Russia and Ukraine signed an agreement in 1997 that allowed Moscow to keep its Black Sea fleet in Crimea's port of Sevastopol, which housed the fleet during Soviet times, for 20 years.

Some 16,000 Russian sailors and 380 Russian warships are currently based in the port.

Ukraine wants to the join NATO, but the military alliance is insisting on tough military reforms before the former Soviet republic can be considered for membership.

Kiev signed a partnership accord with NATO in 1997.

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