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Saudi Defence Minister and Deputy Crown Prince, Mohammed bin Salman (R) walks with US Secretary of Defense Ashton Carter during the Gulf Cooperation Council (GCC) defence Ministrial summit in Riyadh, on April 20, 2016. / AFP / FAYEZ NURELDINE (Photo credit should read FAYEZ NURELDINE/AFP/Getty Images)

Saudi Defence Minister and Deputy Crown Prince, Mohammed bin Salman (R) walks with US Secretary of Defense Ashton Carter during the Gulf Cooperation Council (GCC) defence Ministrial summit in Riyadh, on April 20, 2016. / AFP / FAYEZ NURELDINE        (Photo credit should read FAYEZ NURELDINE/AFP/Getty Images)

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RIYADH, SAUDI ARABIA - DECEMBER 29: Saudi Defense Minister Mohammad bin Salman Al Saud (R) meets Kuwaiti Deputy Prime Minister and Minister of Defense Sheikh Sabah al-Khaled al-Sabah (L) in Riyadh, Saudi Arabia, on December 29, 2016. (Photo by Bandar Algaloud / Saudi Royal Council / Handout/Anadolu Agency/Getty Images)

RIYADH, SAUDI ARABIA - DECEMBER 29: Saudi Defense Minister Mohammad bin Salman Al Saud (R) meets Kuwaiti Deputy Prime Minister and Minister of Defense Sheikh Sabah al-Khaled al-Sabah (L) in Riyadh, Saudi Arabia, on December 29, 2016. (Photo by Bandar Algaloud / Saudi Royal Council / Handout/Anadolu Agency/Getty Images)

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Tribal gunmen loyal to the Huthi movement brandish their weapons on March 26, 2015 during a gathering in Sanaa to show support the Shiite Huthi militia and against the Saudi-led intervention in the country. Warplanes from a Saudi-led Arab coalition bombed Huthi rebels in support of Yemen's embattled president, as regional rival Iran warned the intervention was a 'dangerous' move. AFP PHOTO / MOHAMMED HUWAIS (Photo credit should read MOHAMMED HUWAIS/AFP/Getty Images)

Tribal gunmen loyal to the Huthi movement brandish their weapons on March 26, 2015 during a gathering in Sanaa to show support the Shiite Huthi militia and against the Saudi-led intervention in the country. Warplanes from a Saudi-led Arab coalition bombed Huthi rebels in support of Yemen's embattled president, as regional rival Iran warned the intervention was a 'dangerous' move. AFP PHOTO / MOHAMMED HUWAIS        (Photo credit should read MOHAMMED HUWAIS/AFP/Getty Images)

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TOPSHOT - Armed Yemeni tribesmen from the Popular Resistance Committees, supporting forces loyal to Yemen's Saudi-backed President Abedrabbo Mansour Hadi, fire as they hold a position in the area of Sirwah, west of Marib city, on December 18, 2015. A Yemen ceasefire appeared to have collapsed as government forces captured two towns from rebels and an allied Arab coalition accused insurgents of escalating the conflict by firing ballistic missiles. / AFP / ABDULLAH AL-QADRY (Photo credit should read ABDULLAH AL-QADRY/AFP/Getty Images)

TOPSHOT - Armed Yemeni tribesmen from the Popular Resistance Committees, supporting forces loyal to Yemen's Saudi-backed President Abedrabbo Mansour Hadi, fire as they hold a position in the area of Sirwah, west of Marib city, on December 18, 2015. A Yemen ceasefire appeared to have collapsed as government forces captured two towns from rebels and an allied Arab coalition accused insurgents of escalating the conflict by firing ballistic missiles.

 / AFP / ABDULLAH AL-QADRY        (Photo credit should read ABDULLAH AL-QADRY/AFP/Getty Images)

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Saudi army artillery fire shells towards Yemen from a post close to the Saudi-Yemeni border, in southwestern Saudi Arabia, on April 13, 2015 . Saudi Arabia is leading a coalition of several Arab countries which since March 26 has carried out air strikes against the Shiite Huthis rebels, who overran the capital Sanaa in September and have expanded to other parts of Yemen. AFP PHOTO / FAYEZ NURELDINE (Photo credit should read FAYEZ NURELDINE/AFP/Getty Images)

Saudi army artillery fire shells towards Yemen from a post close to the Saudi-Yemeni border, in southwestern Saudi Arabia, on April 13, 2015 . Saudi Arabia is leading a coalition of several Arab countries which since March 26 has carried out air strikes against the Shiite Huthis rebels, who overran the capital Sanaa in September and have expanded to other parts of Yemen. AFP PHOTO / FAYEZ NURELDINE        (Photo credit should read FAYEZ NURELDINE/AFP/Getty Images)