Russia's top diplomat said Monday that the price of halting the deployment of Russian troops in the Crimea would be the restoration of a deal reached last month between Ukraine's ousted President and opposition leaders.
Foreign Minister Sergey Lavrov told a U.N. Human Rights Council session in Geneva that Ukraine should return to an agreement signed last month by pro-Russian President Viktor Yanukovych -- but not by Moscow -- to hold early elections and surrender some powers. Yanukovych fled the country February 22 after sealing the pact with the opposition and foreign ministers of France, Germany and Poland.
"Instead of a promised national unity government," Lavrov said of the fledgling new administration in Kiev, "a government of the victors has been created." 
U.S. Secretary of State John Kerry was headed to Kiev late Monday in an expression of support for Ukraine's sovereignty, and the EU threatened a raft of punitive measures as it called an emergency summit for Thursday. The Pentagon said it was suspending exercises and other activities with the Russian military, and a senior U.S. officials said the U.S. would not move forward with meetings designed to deepen the trade relationship between the two countries. Lacking authorization to speak publicly about the trade meetings, the official requested anonymity.
Earlier Monday, Ukraine officials claimed 16,000 Russian troops had been deployed in the Crimea, a sign of widening military intervention in the flashpoint peninsula.
 “Approximately 16,000 Russian troops have been deployed in Crimea by the military ships, helicopters, cargo airplanes from the neighboring territory of the Russian Federation,” the permanent mission of Ukraine to the United Nations wrote in a letter.  “The Russian troops keep taking their attempts to seize, block and control crucial governmental and military objects of Ukraine in Crimea: the Parliament in Crimea, all civil and military airports, means of communications, radio stations, customs service, military and coast guard bases and headquarters of the Ukraine’s navy in Crimea.”
The letter also claims Russian forces used stun grenades against Ukrainian soldiers, and said Ukrainian ships had been blocked in Sevastopol Bay by Russian naval vessels. Ukraine also claimed that Russian aircraft twice entered the nation’s airspace, and said the Ukrainian military base in Kerch was surrounded by Russian forces.
But the letter says Ukrainian armed forces are “protecting their staffs, military units and bases, and are not responding to any provocations that occurred over the past days.”
Meanwhile, pro-Russian authorities in Crimea said they’ll cut off water and electricity to Ukrainian soldiers in bases surrounded by Russian forces Monday night, a former Russian lawmaker said, Reuters reported.
Earlier Monday, armed men seized a Ukrainian border checkpoint at a ferry terminal between Russia and Crimea, Reuters reported.
Russians had been surrounding the ferry terminal for days, but had not taken control of Ukraine's border guard station until now, Reuters said, citing Ukrainian border guards.
The troops seized the checkpoint after guards tried to stop two buses carrying seven armed men, and the next ferry brought three truckloads of soldiers across, a border guard spokesman said, Reuters reported.
Those developments came after heated exchanges at an emergency meeting of the United Nations Security meeting on Monday, in which the U.S. ambassador said there was no justification for Russia’s military intervention in Ukraine, while her Russian counterpart said the ousted Ukrainian president had asked Russia to use troops.
Russian U.N. envoy Vitaly Churkin quoted Yanukovych, who fled to Russia, as saying "the life and security and the rights of people particularly in the southeast part in Crimea are being threatened," and continued: "So under the influence of Western countries there are open acts of terror and violence."
If true, the request would be a reversal for Yanukovych, who had said Friday he would not ask for Russian forces.
But U.S. Ambassador Samantha Power said there was no evidence that ethnic Russians in the region were under direct threat.
Meanwhile, despite an report by Interfax that Russian forces had demanded all Ukrainian troops in Crimea surrender by 5:00 a.m. local time Tuesday or face “a real assault," the deadline passed without incident. 
A Russian Black Sea Fleet official later told Interfax that there are no plans to launch an assault on Ukrainian military units in Crimea and the fleet did not set an ultimatum to surrender, according to Reuters.
Despite the claims, the EU is threatening to freeze visa liberalization and economic cooperation talks and boycott the G8 summit in Russia's Sochi if Moscow does not back off in Ukraine.
French Foreign Minister Laurent Fabius said the EU would give Russia until an emergency summit of EU leaders is held on Thursday to show clear signs of goodwill, including a willingness to open talks and a withdrawal of Russian troops to their barracks in the Crimea.
If not, Fabius said the EU would start implementing punitive measures.
The uncertainty of the situation going forward roiled global financial markets Monday, as Russia continued to impose its military presence on Ukraine.
Ukrainian Defense Ministry spokesman Maksim Prauta said Monday that four Russian navy ships were blocking Ukraine's anti-submarine warship Ternopil and the command ship Slavutych in Sevastopol's harbor. He said the Russians ordered the crew to surrender within the hour or face Russians storming and seizing the ships and crew.
Ukrainian Prime Minister Arseniy Yatsenyuk insisted that Crimea remains Ukrainian territory despite the presence of thousands of Russian troops who have secured control over the region without suffering any casualties or firing a shot.
"Any attempt of Russia to grab Crimea will have no success at all. Give us some time," he said at a news conference with British Foreign Secretary William Hague, who is visiting Kiev.
"For today, no military options [are] on the table," he said, adding that what they urgently need is an economic and political support.
NATO is urging Russia to pull back its forces and seek a peaceful resolution through dialogue with Ukraine.
Ukraine is not a NATO member, which means the United States and Europe are not obligated to come to its defense. But Ukraine has taken part in some alliance military exercises and contributed troops to its response force.
Russia has long wanted to reclaim the lush Crimean Peninsula, part of its territory until 1954. Russia's Black Sea Fleet pays Ukraine millions annually to be stationed at the Crimean port of Sevastopol and nearly 60 percent of Crimea's residents identify themselves as Russian.
The Associated Press contributed to this report.