Antonio Guterres assumes the reins of the United Nations on Sunday hoping to breathe new life into the world body, in the wake of its impotence over Syria's humanitarian catastrophe.

The Portuguese former prime minister, 67, will become the first onetime head of government to lead the UN, succeeding South Korea's Ban Ki-moon for a five-year term.

His unanimous election has energised UN diplomats who see him as a skilled politician who may be able to overcome the divisions crippling the United Nations.

One Western ambassador regretted only that a woman wasn't picked to take the post for the first time, adding with a smile that "except for the gender, he is perfect."

Guterres faces a monumental task grappling with complex crises in Syria, South Sudan, Yemen, Burundi, North Korea and elsewhere - overseeing a clunky entrenched bureaucracy and a bitterly divided Security Council that will leave him little room to maneuver.

-AFP