Antonio Guterres sworn in as 9th UN Secretary General on Monday

United Nations: Former Portuguese prime minister Antonio Guterres was on Monday sworn in as the ninth UN Secretary-General.

Guterres, 67, succeeded Ban Ki-moon as the chief of the world body.

He was administered the Oath of Office by UN General Assembly president Peter Thomson at a special plenary of the 193-member General Assembly.

In October, the 15-nation UN Security Council had sent his name to the Assembly for final approval.

The former UN refugee chief will take over from Ban on January 1.

Ban's second five-year term ends on December 31.

During the special plenary meeting, speakers paid tribute to Ban.

The former UN High Commissioner for Refugees had remained the front-runner in the election to choose the successor to Ban.

Following his election, Guterres vowed to work as a "convener" and "bridge-builder" to help find solutions to the world's pressing challenges.

"I am fully aware of the challenges the UN faces and the limitations surrounding the Secretary-General," Guterres said in his first address following his appointment as the 9th UN Secretary General, PTI reported.

Guterres vowed to carry out reforms to improve the world body. "The UN must be ready to change," he said.

Ban Ki-moon led the UN for two terms from 2007.