Russia's Black Sea Fleet boosted security at its navigational facilities on Sunday amid a dispute with Ukraine over a lighthouse linked to the fleet in the Crimean city of Yalta, a navy spokesman said.
"Security at the Black Sea Fleet's navigational facilities has been tightened," Igor Dygalo was quoted by the Interfax news agency as saying. "If further attempts are made to seize the fleet's facilities or to enter them, security will be tightened even further."
Russia's move came after Ukraine threatened to take over all the navigational facilities of the Black Sea Fleet.
The two countries signed an accord in 1997 on dividing up the Soviet Black Sea Fleet. Under the deal, Russia leases the Sevastopol port in Ukraine's Crimea peninsula to base its ships until 2017.
The dispute emerged on Friday when staff of a Ukrainian state company seized the lighthouse and denied Russian servicemen access to the lighthouse.
Russian navy officials have accused Ukraine of violating the lease agreement that allows the Black Sea Fleet to use Ukraine's facilities.
The Russian Foreign Ministry on Sunday called for dialogue with Ukraine, saying only a constructive dialogue could yield mutually compatible solutions to disputes between the two countries.
During a recent row over natural gas prices, Ukraine threatened to raise the annual rent Russia pays for leasing the Sevastopol port. Russia rejected it as unacceptable.