Ukraine defense officials have accused Russia's military of demanding that Ukrainian forces in Crimea surrender by 10 p.m. ET, lest Russian forces "start a real storm" at Ukrainian bases in the strategic peninsular region. But NBC News could not immediately confirm the report, and a Russian spokesman told the news agency Interfax that no such ultimatum had been issued. Meanwhile Monday, Reuters reported that according to Ukrainian border guards, Russian forces had begun moving troops into Crimea by ferry, after seizing control of the border post on the Ukrainian side of the waterway — days after Russians who seized the isolated but strategic, and heavily ethnically Russian, Black Sea peninsula had first surrounded the ferry terminal. The latest movements came after Ukraine mobilized for war on Sunday after Russian President Vladimir Putin declared he had the right to invade his neighbor to protect Russian citizens in Crimea, triggering the greatest confrontation between Russia and the West since the Soviet Union collapsed.