Just released from Vedomosti, google translated for most linguistic impact:

Russian Defense Ministry denies reports appeared that the Ukrainian military in Crimea delivered an ultimatum . Today the agency " Interfax-Ukraine" reported, citing a source in the Defense Ministry of Ukraine , that the commander of the Black Sea Fleet of Russia Alexander Vitko an ultimatum Ukrainian soldiers in the Crimea . According to the source agency , if, prior to 5:00 am Tuesday Ukrainian soldiers " do not give up , start a real assault units and parts of the Ukrainian Armed Forces around the Crimea." The official representative of the Russian Defense Ministry called Message agency " utter nonsense " and said that any ultimatums Ukrainian military in the Crimea was not put. Head of Naval Forces of Ukraine in Sevastopol Crimean authorities busy loyal soldiers about half ( in its territory is located a few buildings ), another half remains under control VMSU says Ukrainian officer , with no clusters of armed men and now there is no activity , but about the ultimatum he heard nothing.

And the more formal narrative from Reuters, which broke the original story, now being denied:

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 Defence 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."

Hmmmm, whom to believe...