President Barack Obama talks on the phone in the Oval Office with Russian President Vladimir Putin about the situation in Ukraine, March 1, 2014. The White House said Obama and Putin spoke by phone for 90 minutes, their second phone call in the past eight days over Ukraine, an escalating crisis that is presenting a new challenge to already strained US-Russian relations. Pete Souza/White House/Reuters
Russian Foreign Minister Sergey Lavrov (l.) and US Secretary of State John Kerry stand together before a meeting at Winfield House in London, March 14, 2014. With Crimea in Russia's pocket, the world anxiously awaits Russian President Putin's next move. Putin has held regular conversations with President Obama and other Western leaders - and Lavrov met with Kerry for six hours of talks in London last week - with no visible result. Brendan Smialowski/AP
President Obama meets with President Putin in Enniskillen, Northern Ireland, June 17, 2013. Obama and Putin discussed the ongoing conflict in Syria during their bilateral meeting. Evan Vucci/AP
President Obama and Russian President Dmitry Medvedev ride together to lunch in Arlington, Va., June 24, 2010. Pete Souza/White House/AP
President Putin and President George W. Bush speak to the media after their summit meeting outside the Bush family home on Walker's Point in Kennebunkport, Maine, July 2, 2007. Jason Reed/Reuters
President Bill Clinton (l.) and Russian President Boris Yeltsin take in the view of the Hudson River valley outside the home of Franklin D. Roosevelt in Hyde Park, N.Y., Oct. 23, 1995. Yeltsin met with Clinton more than 15 times. Rick Wilking/Reuters
President Clinton wipes away tears of laughter as he leans on President Yeltsin after a remark by Yeltsin during a joint press conference following their talks in Hyde Park, N.Y., Oct. 23, 1995.
President George H.W. Bush and Soviet President Mikhail Gorbachev shake hands as they meet in London, July 17, 1991. Greg Gibson/AP
President Ronald Reagan and Soviet leader Mikhail Gorbachev sign the Intermediate Range Nuclear Forces Treaty and other documents during a ceremony in the White House East Room on Dec. 8, 1987. Reagan and Gorbachev signed the treaty to eliminate all ground-launched, medium-range missiles of both nations, the first true cuts in either nation's arsenal. Barry Thumma/AP
President Reagan acknowledges the crowd after his speech on June 12, 1987, in front of the Brandenburg Gate in West Berlin, where he said 'Mr. Gorbachev, tear down this wall!' Ira Schwartz/AP
Soviet Premier Nikita Khrushchev and President John F. Kennedy talk in the residence of the US Ambassador in a suburb of Vienna on June 3, 1961. The meeting was part of a series of talks during their summit meetings in Vienna. AP
Cuba's leader Fidel Castro (c.) speaks with Soviet Premier Khrushchev as his Foreign Minister Raul Roa looks on at the Hotel Theresa during the United Nations General Assembly in New York on Sept. 20, 1960. The world stood at the brink of Armageddon for 13 days in October 1962 when President John F. Kennedy drew a symbolic line in the Atlantic and warned of dire consequences if Soviet Premier Nikita Khrushchev dared to cross it during the Cuban Missile Crisis. Prensa Latina via AP Images/AP
Sweden's top military official said that they do not know who owns the submarine, which triggered the country's largest mobilization since the cold war. But Stockholm plans to upgrade its naval security in response.
ByNiklas Pollard, Reuters
Claudio Bresciani/TT News Agency/Reuters
Sweden has proof that a small foreign submarine was operating illegally in its waters last month, its top military officer said on Friday after a mysterious episode that triggered the country's biggest military mobilization since the cold war.