US President Donald Trump's Defense Secretary arrived in the United Arab Emirates today for talks with one of Washington's closest allies in the Middle East. <br/><br/>Jim Mattis, on his debut trip to the region as Pentagon Chief, is expected to meet Abu Dhabi Crown Prince Sheikh Mohammed bin Zayed al-Nahayan and US embassy representatives. <br/><br/>In late January, Trump and the Crown Prince spoke by telephone and the White House said they had discussed a proposal for safe zones for Syrian refugees displaced by the conflict.<br/><br/>Mattis, a retired Marine general who is reviewing U.S. war plans against Islamic State in Syria and Iraq, is a familiar figure to Gulf Arab rulers.<br/><br/>The United Arab Emirates is also a key U.S. ally in the fight against al Qaeda in Yemen.