President Viktor Yushchenko, back from a visit to Georgia to offer support in its confrontation with Moscow, on Wednesday introduced tougher regulations on the movements of Russian warships based in his ex-Soviet state.
Russia said the move dealt "another blow" to already difficult relations between the two neighbours.
Long at odds with Moscow over its campaign to seek NATO membership, Ukraine's pro-Western leadership has issued statements backing Georgia's position and urging Russia to withdraw from the country's territory.
The foreign ministry this week reserved the right to prevent ships from the Black Sea fleet returning to base in Ukraine's Crimea peninsula if they had taken part in military action.
On Wednesday, the president issued a decree ordering Russia to advise 72 hours in advance of any movement by its ships, aircraft and personnel based in Ukraine. Ukrainian authorities would be empowered to alter its travel plans.
A statement issued after a meeting of the Security Council said the presence of foreign warships "poses a potential threat to Ukraine's national security particularly if parts of Russia's Black Sea Fleet are used against third countries".
In Moscow, Russia's foreign ministry expressed "bewilderment" at a decision it said "failed to observe even elementary diplomatic niceties".
"This unilateral step deals yet another blow to the process of negotiations around the Black Sea Fleet and, in a broader sense, to bilateral relations as a whole," it said.
Yushchenko attended a mass rally in Tbilisi on Tuesday in support of Saakashvili, along with the leaders of other countries once in the Soviet orbit -- the Baltic states of Estonia, Latvia and Lithuania, and Poland.
Under a 1997 agreement, Ukraine agreed to lease harbour space in the Crimean peninsula base of Sevastopol until 2017 -- as an exception to a provision in the post-Soviet constitution barring foreign bases from the country.
Yushchenko and other officials say Ukraine has no intention of extending the lease and have called for negotiations to ensure for an orderly departure of the fleet by 2017 -- a position strongly criticised by the Kremlin.
Russia has in the past two weeks also accused Ukraine of encouraging Georgia to engage in "ethnic cleansing" in the separatist region of South Ossetia by selling weapons to Tbilisi. Ukraine denied the allegation.
Last Mod: 14 Ağustos 2008, 15:00