Newly sworn-in UN Secretary-General Antonio Guterres vowed Monday to improve the world body’s ability to respond to global crises after taking the oath of office.

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

“The organisation is the cornerstone of multilateralism and has contributed to decades of relative peace, but the challenges are now surpassing our ability to respond,” Guterres told the General Assembly.

“UN must be ready to change,” he added.

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

The former prime minister of Portugal 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.”

Citizens worldwide are losing confidence in their governments and in global institutions, he said, adding that it was “time to reconstruct relations” between leaders and their people.

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

An engineer by training and practising Catholic, Guterres fought for migrants’ rights over a decade as UN High Commissioner for Refugees from June 2005 to December 2015.

He served as prime minister of Portugal from 1995 to 2002, anchoring his country to the European Union and working to raise living standards.