North Atlantic Treaty Organization (Nato)

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U.S. Secretary of State John Kerry speaks during a news conference at NATO Headquarters in Brussels Tuesday April 1, 2014. (AP Photo/Jacquelyn Martin, Pool)

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U.S. Secretary of State John Kerry, right, meets with Ukrainian Foreign Minister Andriy Deshchytsia before their meeting at NATO Headquarters in Brussels, Tuesday April 1, 2014. (AP Photo/Jacquelyn Martin, Pool)

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U.S. Secretary of State John Kerry speaks during a news conference at NATO Headquarters in Brussels, Tuesday April 1, 2014. (AP Photo/Jacquelyn Martin, Pool)

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U.S. Secretary of State John Kerry, right, shakes hands with Ukrainian Foreign Minister Andriy Deshchytsia before their meeting at NATO Headquarters in Brussels, Tuesday April 1, 2014. (AP Photo/Jacquelyn Martin, Pool)

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U.S. Secretary of State John Kerry speaks during a news conference at NATO Headquarters in Brussels, Tuesday April 1, 2014. (AP Photo/Jacquelyn Martin, Pool)

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U.S. Secretary of State John Kerry speaks during a news conference at NATO Headquarters in Brussels Tuesday April 1, 2014. (AP Photo/Jacquelyn Martin, Pool)

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NATO Secretary General Anders Fogh Rasmussen gestures during a meeting of the North Atlantic Council at NATO headquarters in Brussels on Tuesday, April 1, 2014. NATO foreign ministers begin a two-day meeting on Tuesday in which they will discuss, among other issues, the situation in Ukraine. (AP Photo/Virginia Mayo)

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NATO Secretary General Anders Fogh Rasmussen gestures while speaking during a media conference ahead of a meeting of the North Atlantic Council at NATO headquarters in Brussels on Tuesday, April 1, 2014. NATO foreign ministers begin a two-day meeting on Tuesday in which they will discuss, among other issues, the situation in Ukraine. (AP Photo/Virginia Mayo)