Antonio Guterres greets a Syrian child during a visit to Lebanon in 2014. [Photo by Bilal Hussein/AP]

The Security Council unanimously agreed on Wednesday that Portugal's former prime minister Antonio Guterres should be the next secretary-general of the United Nations.

Russia's UN Ambassador Vitaly Churkin made the announcement to reporters surrounded by the 14 other council ambassadors after they held a sixth informal poll of the 10 candidates behind closed doors.

Churkin announced that the council will hold a formal vote on Thursday morning to recommend Guterres to the 193-member General Assembly, which must approve a successor to Ban Ki-moon, whose second five-year term ends on Dec 31.

"We wish Mister Guterres well in discharging his duties as the secretary-general of the United Nations in the next five years,"Churkin said.

By tradition, the job of secretary-general has rotated among regions. Asia, Africa, Latin America and Europe have all held the post. East European nations, including Russia, argue that they have never had a secretary-general and it was their turn.

There has also never been a woman secretary-general, and more than 50 nations and many others campaigned to elect the first female UN chief.

But Guterres, 67,who served as prime minister from 1995 to 2002 and served as the UN's high commissioner for refugees until December, topped all six polls despite being a man from Western Europe.

For the first time this year, the General Assembly's members held two-hour question-and-answer sessions with all 13 candidates who entered the race, and in the eyes of many diplomats, Guterres performed best.