MOSCOW - Russia's Black Sea Fleet has not issued an ultimatum to Ukrainian forces in Crimea to surrender by 5 a.m. on Tuesday or face an assault, Interfax news agency quoted an official at the fleet's headquarters as saying.Russia's Black Sea Fleet has a base in Crimea and Moscow has effectively established control over the peninsula, which is part of Ukraine.Interfax quoted an unnamed source in the Ukrainian Defense Ministry earlier on Monday as saying a deadline to surrender at 0300 GMT had been set by the Black Sea Fleet's commander.The same news agency later quoted an unnamed representative at the fleet's headquarters as saying no assault was planned, adding: "This is complete nonsense."