Russia made a rare admission on Sunday that it had violated Ukrainian law by trying to transport cruise missiles outside its Black Sea naval base of Sevastopol, Russian news agency RIA reported.

Earlier this month, Ukrainian police blocked a convoy of Russian trucks from leaving the base to transport missiles through the Ukrainian city, adding to tensions between the two ex-Soviet states.

"We acknowledged there were violations of basic agreements on basing the Russian Black Sea fleet in Sevastopol," RIA quoted Russian navy commander Admiral Vladimir Vysotsky as saying.

"We believe those were serious violations," he said. "Those responsible will be punished, quite heavily at that."

Vysotsky, who was in Sevastopol to mark Russia's annual Navy Day, said the paperwork dealing with the convoy had not been not done properly.

Moscow leases a base for its Black Sea Fleet in Sevastopol, a port in the Crimea peninsula populated mainly by ethnic Russians. The status of the base has been a thorn in relations between Moscow and Kiev since Ukraine's independence in 1991.

Ukraine, which has committed itself to closer ties with the West and whose President Viktor Yushchenko is pressing for NATO membership, wants Russia to close the base in 2017 as stipulated by existing agreements.

Russia sees NATO expansion up to its borders as a threat to its security and was troubled by joint Ukrainian-NATO naval exercises last July in the Black Sea.

Tensions hit a peak the following month, when Russia sent warships from the base to Georgia during its five-day war with the Caucasus state. Yushchenko backed Georgia in the conflict.

The two sides have traded accusations over a series of incidents concerning the base and in the past have been reluctant to acknowledge any guilt.

Relations are also marred by disputes over Russia's gas supply to Ukraine and its transit to Europe.