Simferopol , Ukraine ( CNN ) -- The standoff in Ukraine 's Crimea region is a strange one , where soldiers appear to be standing around amid an air of calm . They wear no military insignia , but there 's little doubt about who they are . Russian forces `` have complete operational control of the Crimean peninsula , '' a senior U.S. administration official told CNN , with estimates of 6,000 Russian ground and naval forces in the region . A law is being considered in the Russian parliament that would allow Crimea to be annexed , according to the parliament 's website . Armed men are blocking 10 Ukrainian military and naval bases in Crimea , the newly appointed naval commander of Ukraine , Rear Adm. Serhei Gayduk , told a Ukrainian TV station . Many ethnic Russians live in Crimea , where support for Russia is strong . Part of Russia 's navy -- the Russian Black Sea Fleet -- has a base in Crimea 's city of Sevastopol that has been there for 230 years . In Crimea 's capital , Simferopol , soldiers were circling government buildings and patrolling some streets , but their presence did not feel invasive , CNN correspondent Diana Magnay reported Monday . It appears that there is a `` war of information '' in the region `` between those who watch Russian state TV and those who are getting their news from the West , none of them listening to the calls from Kiev for unity in this country , '' Magnay reported . It has been , Magnay says , `` a very low-key kind of invasion . '' Crimea 's First Vice-Premier Rustam Temirgaliyev also described the situation as quiet , Russian state news agency ITAR Tass reported on Monday . `` Despite hysteria in Ukraine 's central media , the situation on the peninsula remains absolutely calm . No conflicts have flared up in Crimea over the past 24 hours . Crimea has preserved its inter-ethnic peace , '' Temirgaliyev said , according to ITAR Tass . The calmness contrasts with reports that Russia has issued an ultimatum to Ukrainian forces in Crimea to clear out by 5 a.m. Tuesday or face a `` military storm , '' according to a report from Russian state-run news agency Interfax , citing a Ukrainian Defense Ministry source . Additionally , Ukrainian Defense Ministry spokesman Vladislav Seleznyov told CNN that Russia 's Black Sea fleet commander went aboard a blocked Ukrainian warship in Sevastopol harbor on Monday and issued an ultimatum : Swear allegiance to the new Crimean authorities , surrender , or face an attack . The Russian commander , Aleksandr Vitko , did not mention a deadline , Seleznyov said . But Russia denies plans to storm the Ukrainian military units in Crimea , Interfax said , citing an unidentified spokesman for the Russian Black Sea Fleet . Interfax said the spokesman called these reports `` utter rubbish . '' `` We have gotten used to hearing claims that we are conducting military operations against our Ukrainian colleagues , '' said the spokesman , adding , `` Attempts to set us against each other will fail . '' Meanwhile , Seleznyov told CNN that up to 12 trucks full of Russian troops have crossed into the eastern Crimean city of Kerch from Russia . Additionally , Ukrainian Border Service Assistant Chief Col. Sergei Astakhov described Russian troop movements by ferry from Russia across the Strait of Kerch in a phone conversation . Astakhov said the first two ferries carrying armed men were navigating toward the ferry dock and border post in Kerch . As the ferries approached the port , 10 heavily armed troops from the Russian Black Sea Fleet attacked the border post from land and used force to overwhelm the Ukrainian border guards , Astakhov said . The account of the attack contradicts the calm scene that CNN correspondents had observed in Kerch earlier Monday . Close to 100 men in green uniforms , carrying weapons such as AK-47s , lingered outside the main entrance to the ferry port Monday . Soldiers around there were not masked -- they were relaxing , eating and drinking tea , CNN 's Ben Wedeman reported . Half the soldiers were sitting around and waiting , with some standing and others spaced out every 100 meters . They appeared not to be on high alert . One Ukrainian soldier with an insignia remained by the entrance where cars enter the ferry port . Three six-wheeled military trucks , used for transporting troops , have black license plates indicative of Russian forces based in Crimea , per the agreement between Ukraine and Russia . An officer who wished to be identified only as Alexander , wearing a hat with the Russian Black Sea Fleet insignia , told CNN he and others from the Sevastopol naval base had been deployed outside the ferry port since Saturday . If they were n't there , he said , `` there would be a civil war in Ukraine . '' Alexander said the troops are there to protect their Ukrainian brothers from those who seized power locally in Kiev . Ukrainians gave them places to stay and shower , and locals have brought them food , he said . The troops will stay in Kerch until Crimea decides what it wants to do , Alexander said . Crimea is the last major stronghold of opposition to the new political leadership in Ukraine . The country 's President , Viktor Yanukovych , was ousted February 22 after months of anti-government protests reached a bloody climax . Street clashes between demonstrators and security forces left more than 80 dead . CNN 's Clare Sebastian , Elwyn Lopez , Marie-Louise Gumuchian , Susanna Capelouto , Dana Ford and journalist Emir Shevkiev contributed to this report .
NEW : Crimea 's first vice-premier says situation is quiet . NEW : Ukrainian border official describes attack in Kerch . Conflicting messages are coming from Kiev and Moscow . Crimea is last major stronghold opposing the new political leadership in Ukraine .