WASHINGTON (MarketWatch) -- Russia's Black Sea Fleet hasn't issued an ultimatum to Ukrainian forces in Crimea to surrender by 5 a.m. Tuesday or face an assault, Reuters reported, citing the Interfax news agency. Earlier, Ukraine said Russian forces controlling Crimea were demanding the crew of two Ukrainian warships surrender or face seizure by the Russian navy. Interfax quoted an unnamed representative at the Black Sea Fleet's headquarters saying no assault was planned and adding "This is complete nonsense."