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US Secretary of Defense James Mattis (l) arrives at the Pentagon on January 21, 2017, for his first day of work and is greeted by Chairman of the Joint Chiefs of Staff General Joseph Dunford in Washington, DC. / AFP / PAUL J. RICHARDS (Photo credit should read PAUL J. RICHARDS/AFP/Getty Images)

US Secretary of Defense James Mattis (l) arrives at the Pentagon on January 21, 2017, for his first day of work and is greeted by Chairman of the Joint Chiefs of Staff General Joseph Dunford in Washington, DC. / AFP / PAUL J. RICHARDS        (Photo credit should read PAUL J. RICHARDS/AFP/Getty Images)

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Russia's Prime Minister Vladimir Putin (L) speaks with ExxonMobil President and Chief Executive Officer Rex Tillerson during the signing of a Rosneft-ExxonMobil strategic partnership agreement in Sochi on August 30, 2011. Russia's oil champion Rosneft and US ExxonMobil clinched a global deal worth up to half-a-trillion dollars that will see the US supermajor take BP's place in pioneering Arctic exploration work. AFP PHOTO / RIA NOVOSTI / POOL / ALEXEY DRUZHININ (Photo credit should read ALEXEY DRUZHININ/AFP/Getty Images)

Russia's Prime Minister Vladimir Putin (L) speaks with ExxonMobil President and Chief Executive Officer Rex Tillerson during the signing of a Rosneft-ExxonMobil strategic partnership agreement in Sochi on August 30, 2011. Russia's oil champion Rosneft and US ExxonMobil clinched a global deal worth up to half-a-trillion dollars that will see the US supermajor take BP's place in pioneering Arctic exploration work.  AFP PHOTO / RIA NOVOSTI / POOL / ALEXEY DRUZHININ (Photo credit should read ALEXEY DRUZHININ/AFP/Getty Images)