KIEV, Aug. 13 (Xinhua) -- Ukrainian President Viktor Yushchenko signed a decree on Wednesday imposing new restrictions on Russia's Black Sea fleet, which is based in the Ukrainian port of Sevastopol.

　　The restrictions included a requirement that the Black Sea fleet seek the permission of Ukraine's armed forces at least 72 hours prior to ships or aircraft crossing the Ukrainian border, said the decree.

　　If Russia does not fulfill the new requirements, Ukraine may demand that naval ships and aircraft of the Black Sea fleet leave Ukraine's territory immediately, according to the decree.

　　The move ratcheted up tensions between Russia and Ukraine, which has given political support to Tbilisi during Russia's military conflict with Georgia.

　　However, the Ukrainian president's decree will not apply to the ships of the Black Sea Fleet currently off the coast of Georgia.

　　"It is not a retroactive act. Therefore, no legal grounds unfortunately exist today to demand a liability from the Black Sea Fleet crews," First Deputy presidential chief of staff Oleksandr Shlapak said at a press briefing in Kiev on Wednesday.

　　"This situation demonstrates how imperfect the Ukrainian legislation is," he added.

　　Russia has maintained its Black Sea fleet base in Sevastopol since the 1991 Soviet collapse and the current Russian lease on the facility expires in 2017.