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The United States took another punitive measure against Russia Tuesday, announcing it would not participate in a G8 Summit scheduled for Sochi in June unless Moscow reversed course on Ukraine, Reuters reported.

The move followed an hour-long phone conversation between President Obama and West German Chancellor Angela Merkel that senior administration officials told Fox News focused on trying to construct a diplomatic off-ramp to get Russian President Vladimir Putin to de-escalate the situation in Ukraine.

The White House released a statement saying the two leaders “agreed on the importance of de-escalating the situation, including through the deployment international observers and human rights monitors, and of initiating direct talks between Russia and Ukraine.”

The U.S. will boycott the Sochi G8 summit unless Moscow reverses its position on Ukraine, Reuters quoted a senior administration official as saying.

Officials acknowledged to Fox News that Europeans are skeptical of sanctions against Russia that may harm European economies, but these allies are also concerned that without sanctions, the situation in Ukraine could escalate.

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    Pressed on any potential military action if Putin takes more territory, the officials said they still see no scenario involving military action of any kind

    Earlier Tuesday, at a press conference, Putin insisted that none of his troops had moved into Crimea -- a statement that stunned U.S. Secretary of State John Kerry.

    When informed by a reporter of Putin's claim, Kerry -- who arrived in Kiev on Tuesday -- smiled and said, "He really denied there were troops in Crimea?"

    Putin's claim came as Ukraine's interim Prime Minister Arseny Yatseniuk said that ministers from his country and their Russian counterparts have started holding talks in a bid to ease tensions on the disputed Crimean Peninsula.

    In other developments:

    • Kerry, who is visiting Kiev to show support for the country’s new leaders, called Russia’s response to the Ukrainian crisis an “act of aggression.”

    • Kerry said it was “incredibly moving” to visit the sites where dozens of protesters were killed during anti-government demonstrations that led to President Viktor Yanukovych’s ouster.

    • Ukraine’s border guard service says two Russian navy ships have blocked off both ends of a strait that separates Russia and the Crimea region, Reuters reports.

    • Turkey’s Air Force revealed Tuesday that it scrambled eight F-16 fighter jets a day earlier after a Russian surveillance plane flew parallel along its Black Sea coast, according to Reuters.

    • The White House has announced a $1 billion package of energy aid, training for financial and election institutions, and anti-corruption efforts for Ukraine.

    Putin, speaking at a news conference at his residence outside Moscow on Tuesday, denied that the troops guarding Ukrainian military installations across Crimea were regular Russian troops, claiming that they were "local self-defense forces." Many of the uniforms on those troops lack identifying insignia, but their vehicles and uniforms appear to be Russian. Putin shrugged the accusation off, saying "The post-Soviet space is full of such uniforms."

    Putin said Tuesday that Moscow reserved the right to protect ethnic Russians in Ukraine by any means necessary, but added that force would be used only as a last resort. His remarks were his first public comments on the situation in Ukraine since Yanukovych fled Kiev on February 22. The Russian leader accused the West of using Yanukovych's decision in November to ditch a pact with the 28-nation European Union in favor of closer ties with Russia to encourage the months of protests that drove him from power.

    Putin said that Yanukovych has no political future and claimed that the former Ukrainian leader would have been killed if Russia had not granted him protection. Yanukovych is wanted by Ukraine's interim government on charges of planning the mass murder of civilians during the recent protests. At least 82 people were killed in Kiev in clashes between protesters and security forces prior to Yanukovych's flight into Russia.

    Putin blamed Ukraine's opposition for the ongoing crisis, calling it an "unconstitutional coup” and “armed seizure of power."

    He went on to say that Ukraine's interim president, parliament speaker Oleksandr Turchynov, was "not legitimate. From the legal perspective it is Mr. Yanukovych who is president." Yanukovych fled Kiev one day after reaching an agreement with leaders of the opposition that was brokered by the foreign ministers of France, Germany, and Poland. Earlier this week, Yanukovych was granted protection by Russia.

    Yatseniuk told reporters Tuesday that between Russia and Ukraine, “consultations have started at the level of ministers,” but did not elaborate, according to Reuters.

    Kerry, meanwhile, said the United States will stand by Ukrainian people “as they build the strong, sovereign and democratic country they deserve.”

    U.S. officials traveling with Kerry told The Associated Press that the Obama administration is considering slapping Russia with unspecified economic sanctions as soon as this week. Kerry said Tuesday that it was “quite remarkable” to see the barricades, barbed wire and bullet holes in street lamps in Kiev.

    In response to threats of sanctions, Putin said that the West should be bear in mind that it will also suffer damage from potential sanctions, which he called "counterproductive and harmful."

    Earlier Tuesday, the Kremlin said Putin had ordered tens of thousands of Russian troops participating in military exercises near Ukraine's border to return to their bases. The massive military exercise in western Russia involving 150,000 troops, hundreds of tanks and dozens of aircraft was supposed to wrap up anyway, so it was not clear if Putin's move was an attempt to heed the West's call to de-escalate the crisis.

    As part of the change of power in Ukraine, early elections have been scheduled to take place May 25, but Putin said that Russia would not recognize the results of those elections if they were held under what he called "such terror as we see now."

    Putin echoed remarks made by Russian Foreign Minister Sergey Lavrov Monday at a United Nations forum in Geneva in which Russia's top diplomat said that the price of halting Russian action in Crimea was reinstating the terms of the February 21 agreement, which called for early elections and limited Yanukovych's powers, but did not remove him from office.

    Ukraine’s leadership has accused Moscow of a military invasion in the Crimean Peninsula. But the Kremlin, which does not recognize the new Ukrainian leadership, insists it made the move in order to protect Russian installations and its citizens living there.

    There have been no reports of fighting or casualties since the Russian troop deployments in Crimea began this past Friday. However, there have been signs of increasing tension as pro-Russian troops fired warning shots to ward off protesting Ukrainian soldiers at the Belback Air Base in Sevastopol. A senior Russian Army officer also told a group of angry Ukrainian marines in Feodosia that he was given orders from Putin to disarm them and wanted them to lock their weapons in a warehouse, The Guardian reports.

    Ukrainian border guards say Russian armored vehicles were spotted on the Russian side of the Kerch Strait, which separates Russia and Crimea, but the Russian military has not confirmed the sightings, Reuters reports.

    In Brussels, meanwhile, the ambassadors of NATO's 28 member nations will hold a second emergency meeting on Ukraine on Tuesday after Poland, which borders both Russia and Ukraine, invoked an article calling for consultations when a nation sees its "territorial integrity, political independence or security threatened," the alliance said in a statement.

    Earlier Tuesday, Russia's agricultural oversight agency issued a statement declaring a reversal of its earlier decision to lift the ban on imports of U.S. pork. It said the existing U.S. system of checks don't guarantee its safety.

    Putin's economic advisor, Sergei Glazyev, said that Russia can develop financial ties with other nations to offset any potential Western sanctions.

    The European Union's foreign ministers on Monday threatened Moscow with halting talks on visa liberalization and negotiations on further economic cooperation unless Russian troops on the Crimean peninsula pull back over the next three days.

    The bloc's heads of state and government will hold an emergency meeting on the situation in Ukraine on Thursday that will decide on imposing the sanctions if there is no de-escalation on the ground, EU foreign policy chief Catherine Ashton said.

    The Associated Press contributed to this report.