United Nations, December 13 (RHC)-- Incoming U.N. Secretary-General Antonio Guterres vowed Monday to improve the world body's ability to respond to global crises after taking the oath of office, saying the United Nations “must be ready to change.” 

The first former head of government at the U.N. helm, Guterres takes over from Ban Ki-moon on January 1st amid bloodshed in Syria and uncertainty following the election in the United States of Donald Trump. 

The 67-year-old socialist politician said the United Nations must "recognize its shortcomings and reform the way it works" and singled out the failure to prevent crisis as the most serious failure. 

Former prime minister of Portugal from 1995 to 2005 and U.N. high commissioner for refugees from 2005 to 2015, Guterres was sworn in during a formal ceremony as Syrian forces were on the verge retaking the entire city of Aleppo in a potential turning point in the six-year war.  He will begin his new post just weeks before Trump moves into the White House. 

In a reference to Trump's shock election victory and the surge in populism worldwide, Guterres said "fear is driving the decisions of many people around the world." 

Guterres laid out three priorities for change during his five-year term: work for peace, supporting sustainable development and internal reforms.