Russia showed no signs of backing down Monday even as world leaders threatened sanctions and sternly rebuked the country for sending troops into Ukraine . At an emergency U.N. Security Council meeting to discuss the unfolding crisis , Ukraine 's envoy asked for help , saying that Russia had used planes , boats and helicopters to flood the Ukrainian peninsula of Crimea with 16,000 troops in the past week . `` So far , Ukrainian armed forces have exercised restraint and refrained from active resistance to the aggression , but they are in full operational readiness , '' Ukrainian Ambassador Yuriy Sergeyev said . As diplomats at the meeting asked Russia to withdraw its troops and called for mediation to end the crisis , Russian Ambassador Vitaly Churkin insisted his country 's aims were preserving democracy , protecting millions of Russians in Ukraine and stopping radical extremists . He said ousted President Viktor Yanukovych remains Ukraine 's elected leader and has asked Russia to send troops . The Russian envoy read a letter from Yanukovych at the U.N. meeting , describing Ukraine as a country `` on the brink of civil war , '' plagued by `` chaos and anarchy . '' `` People are being persecuted for language and political reasons , '' the letter said . `` So in this regard , I would call on the President of Russia , Mr. Putin , asking him to use the armed forces of the Russian Federation to establish legitimacy , peace , law and order , stability and defending the people of Ukraine . '' U.S . Ambassador Samantha Power said Russia 's claims about the situation in Ukraine are untrue and warned that sending military forces `` could be devastating . '' Yanukovych , she said , abandoned his post last month and was then voted out of office by Ukraine 's democratically elected parliament . `` Russian military action is not a human rights protection mission , '' Power said . `` It is a violation of international law . '' Earlier Monday , global stocks slipped on fears things could get worse , and diplomats grasped for a way to stop the situation from escalating . British Foreign Secretary William Hague called the situation Europe 's most serious crisis of the still-young 21st century . And U.S. President Barack Obama said the United States is examining a series of economic and diplomatic steps to `` isolate Russia , '' and he called on Congress to work with his administration on an economic assistance package for Ukraine . Tensions mount . In Crimea , more Russian troops arrived , surrounding military posts and other facilities and taking effective control of the peninsula from Ukrainian authorities . What they planned to do next remained unclear . Analysts told CNN the apparently growing presence of Russian troops in Crimea means there 's a risk the tense standoff could escalate . `` There are lots of unintended consequences when you have armed men staring at each other in places like you do in Crimea , '' said Michael McFaul , the former U.S . Ambassador to Russia . `` So I think we all need to be very vigilant and worry about the worst case scenario , because it 's no one 's interest ... to see all out civil war in this country in the heart of Europe of 50 million people . '' Putin 's moves into Ukraine come as the Russian leader struggles to deal with a political crisis in the neighboring country that did n't unfold as his government hoped , according to Russia analyst Jill Dougherty , formerly CNN 's Moscow bureau chief . `` Putin has been trying to figure out what to do . So now he 's taking these steps , '' Dougherty said . `` And I think that he probably thinks that they 're carefully calibrated . But he really is playing with fire . '' In one ominous incident , a Ukrainian Defense Ministry spokesman said the commander of Russia 's Black Sea fleet boarded a blocked Ukrainian warship and issued a threat . `` Swear allegiance to the new Crimean authorities , or surrender , or face an attack , '' he said , according to the spokesman , Vladislav Seleznyov . But a spokesman for the Russian Black Sea Fleet said there are no plans to storm Ukrainian military units in Crimea , according to the state-run Interfax news agency . And one Crimean official has reportedly described the situation there as quiet . Despite the assurances , stocks fell around the world , with Russian stocks leading the way as investors parsed the day 's developments . Markets declined in Asia , Europe and the United States , where the benchmark Dow Jones fell 153 points Monday . State Department spokeswoman Jen Psaki said Monday that sanctions against Russia were n't just possible , but likely . Ukraine 's shaky new government has mobilized troops and called up military reservists . In Kiev , interim Prime Minister Arseniy Yatsenyuk , who has accused Moscow of declaring war , vowed that his West-leaning government would not give up the region . `` Nobody will give Crimea away . ... There are no grounds for the use of force against civilians and Ukrainians , and for the entry of the Russian military contingent , '' he said . `` Russia never had any grounds and never will . '' A strange scene : Somewhat polite standoff in Crimea . If judged by the numbers , Ukraine 's military loses war with Russia . Worried West . The tensions have worried the West , and Russia 's G8 partners have condemned Moscow 's military buildup in Crimea . The world 's seven major industrialized powers also suspended preparations for the G8 summit in Sochi , Russia , in June . Their finance ministers announced some economic support for cash-strapped Ukraine . `` We are also committed to mobilize rapid technical assistance to support Ukraine in addressing its macroeconomic , regulatory , and anti-corruption challenges , '' the finance ministers said in a written statement . U.S. Secretary of State John Kerry , due in Kiev Tuesday , said several foreign powers are looking at economic consequences if Russia does not withdraw its forces . The United States has suspended upcoming trade and investment talks with Russia due to the events in Ukraine , a spokesman for the U.S. trade representative said Monday . Obama said Monday that Russia should consider international condemnation of its military moves in Ukraine , adding that `` over time , this will be a costly proposition '' due to sanctions and isolation that will result if the situation continues or worsens . Kerry will offer Ukraine a `` specific '' package of U.S. economic aid when he travels to Kiev for talks Tuesday , Obama said . German Chancellor Angela Merkel 's office said Putin had accepted a proposal to establish a `` fact-finding mission '' to Ukraine , possibly under the leadership of the Organization for Security and Co-operation in Europe , and to start a political dialogue . How is the rest of the world reacting ? East vs. West . Ukraine , a nation of 45 million people sandwiched between Europe and Russia 's southwestern border , has been in chaos since Yanukovych was ousted on February 22 after bloody street protests that left dozens dead and hundreds wounded . Anti-government demonstrations started in late November , when Yanukovych spurned a deal with the EU , favoring closer ties with Moscow instead . Ukraine has faced a deepening split , with those in the west generally supporting the interim government and its European Union tilt , while many in the east prefer a Ukraine where Russia casts a long shadow . Nowhere is that feeling more intense than in Crimea , the last big bastion of opposition to the new political leadership . Ukraine suspects Russia of fomenting tension in the autonomous region that might escalate into a bid for separation by its Russian majority . Ukrainian leaders and commentators have compared events in Crimea to what happened in Georgia in 2008 . Then , cross-border tensions with Russia exploded into a five-day conflict that saw Russian tanks and troops pour into the breakaway territories of South Ossetia and Abkhazia , as well as Georgian cities . Russia and Georgia each blamed the other for starting the conflict . Moscow has defended its parliament 's approval of Putin 's use of military force to protect its citizens in the Crimean Peninsula , an autonomous region of eastern Ukraine with strong loyalty to Russia . But Ukraine 's ambassador to the U.N. says Russia 's reasoning for a possible invasion is fake . `` There is no evidence that the Russian ethnic population or Russian-speaking population is under threat , '' Sergeyev told CNN . The Russian parliament , or Duma , is also considering a law that would allow for the annexation of Crimea , according to the parliament 's website . `` Now they are trying to create new legal basis to prove annexation of the territory they 're now occupying , '' Sergeyev said . MAP : How Ukraine is divided .
The United States suspends bilateral trade talks with Yanukovych . Ukraine envoy : Russian has sent hundreds troops into Crimea . Russia says Ukraine asked them to send troops . Former Yanukovych PM asks `` all the world '' for help in stopping Ukraine from losing Crimea .