SEVASTOPOL, Ukraine -- The Russian ministry of defense on Monday dismissed as "total nonsense" a report that its navy had delivered an ultimatum to Ukraine's military to surrender at dawn or face a "real storm," the Russian media reports.
The reported ultimatum came as British Foreign Secretary William Hague on Monday called the standoff in Ukraine the "biggest crisis in Europe of the 21st century."
The warning reportedly came Monday afternoon from Russian Black Sea Fleet Commander Aleksandr Vitko in the Crimean port of Sevastopol.
"If they do not give up by 5 a.m. tomorrow, there will be a real storm of subdivisions and units of Ukraine's military forces all over Crimea," Vitko was quoted by Russia's official Interfax news agency.
A spokesman for the Russia defense ministry dismissed the report as "total nonsense" and said that no such ultimatum had been issued, the state-run RT.com news agency reported.
"We have become accustomed to the daily accusations by the Ukrainian media of carrying out some sort of military actions against our Ukrainian colleagues," Russian Black Sea Fleet representative said, according to RT.com, adding that "those who want to pit us against each other in the Crimea won't succeed."
Amid the conflicting reports, Ukraine said Russian forces controlling the strategic region of Crimea are demanding that the crew of two Ukrainian warships must surrender, the Associated Press reports.
Ukraine's interim prime minister in Kiev remained defiant.
"No one will ever give Crimea to anybody," Ukrainian Prime Minister Arseniy Yatseniuk said at a press conference Monday reported by the Kiev Post. "We realize that the Russian Federation has its interests but we address to Russia: you have no right to protect your interests by violating ours."
Hague, who was speaking to BBC radio from Kiev, said that Russia is now in operational control of Ukraine's Crimean region.
Meanwhile, at a session of the United Nations' Human Rights Council in Geneva, Russian Foreign Minister Sergey Lavrov said: "This is a question of defending our citizens and compatriots, ensuring human rights, especially the right to life.
The dramatic British characterization of events comes as global leaders issued a joint statement Monday on the increasingly fraught political situation in Ukraine and as geopolitical fears spread in earnest to the global investment community.
"We, the leaders of Canada, France, Germany, Italy, Japan, the United Kingdom and the United States and the President of the European Council and President of the European Commission, join together today to condemn the Russian Federation's clear violation of the sovereignty and territorial integrity of Ukraine, in contravention of Russia's obligations under the U.N. Charter and its 1997 basing agreement with Ukraine," the leaders said in the statement.
The USA and other nations have already suspended preparations for a G-8 summit due to be held in Sochi, Russia, in June.
In a bid to reverse a plunge in the ruble — Russia's currency — the Bank of Russia hiked its key interest rate to 7% from 5.5% early Monday. Russia's benchmark Micex index fell as much as 11% and markets across Asia declined sharply. Wall Street is on track to start the week with steep losses.
"Any attempt of Russia to grab Crimea will have no success at all. Give us some time," Britain's Hague said in a separate news conference in Kiev on Monday.
"For today, no military options (are) on the table," he said, adding that what Ukraine urgently needed was economic and political support.
"Real support. Tangible support. And we do believe that our Western partners will provide this support," he said.
Hague said "the world cannot just allow this to happen." But he ruled out any military action.
Russia tightened its military grip on Crimea as troops thought to be sympathetic to Moscow seized a ferry terminal in the city of Kerch. Unidentified soldiers that Ukraine's government has said belong to Russia's military have already taken over airports in Crimea and besieged military bases on the strategic Black Sea peninsula.
Yatsenyuk insisted that Crimea remains Ukrainian territory despite the presence of Russian military.
U.S. Secretary of State John Kerry and European foreign ministers announced plans Sunday for talks in Kiev aimed at easing rising tensions as Ukraine put its military on high alert and appealed for international help against a feared invasion by Russia.
Earlier in the day Ukraine's interim prime minister said that he thought that the danger had passed, saying he'd been assured by Russia's Prime Minister Dmitry Medvedev that Russia was not planning a full-scale invasion of Crimea.
"I think we have passed the peak of the crisis in the relations between Ukraine and Russia. My hope is that the words Russian Prime Minister Medvedev said to me that a decision to send troops has not been adopted are true," Yatseniuk told a meeting of European business leaders in remarks reported by Ukraine's official Interfax news agency.
In Crimea, armed soldiers equipped as professional soldiers but bearing no official insignias, continue to surround Ukrainian military units including the navy's Black Sea fleet which is also based in Sevastopol.
Ukraine's incoming naval commander has announced he has switched allegiance to Crimea's pro-Russia administration. Viktoria Siumar, deputy secretary of Ukraine's National Security and Defense Council in Kiev said Rear Admiral Denis Berezovsky, who Sunday took an oath of allegiance to Crimea's local administration, was fired and is under investigation for treason.
Ukrainian military officials say no Ukrainian servicemen have switched sides to the self-proclaimed Crimean government and laid down arms, Ukraine's Interfax reported.
"Today we are facing absolutely massive amount of misinformation from Russian media that Ukrainian servicemen are laying down the arms," Siumar said.
She said that naval officers in Sevastopol and elsewhere continue to obey orders from Kiev and are not following Berezovsky.
Contributing: Associated Press