Guterres secured 13 votes in favour and two neutral votes in what was the sixth straw poll vote, this time held with colour-coded ballots making clear the sentiment of the five permanent members of the Security Council.

A formal vote will take place at the Security Council on Thursday to confirm the candidacy that will be put to all members of the UN, British Ambassador to the UN Matthew Rycroft wrote on Twitter.

Unofficial information suggests Türk received three votes in favour, including one from a permanent member of the Security Council, eight votes against and two "no opinion" votes, placing eighth among ten candidates.

In his first reaction, Türk wrote on Twitter: "I congratulate Antonio Guterres for the excellent results wish him all success."

Türk told the STA that his candidacy was credible, but noted that the conduct of the Eastern European bloc, ostensibly next in line to name the secretary general, would "probably be the subject of discussion".

"I believe the permanent members of the Security Council wanted to resolve this issue quickly, they have many other issues on their agenda," he said.

President Borut Pahor congratulated Guterres on the election and Türk on his performance.

Türk "presented himself in the best possible way and credibly represented Slovenia in the race," the president told the STA.

Prime Minister Miro Cerar and Foreign Minister Karl Erjavec plan to comment after the formal vote on Thursday.

Guterres, who led the UN refugee agency for 10 years, had been the front runner from the earliest stages of the race and it is widely expected he will be endorsed by the General Assembly to take over on 1 January 2017.

Türk had been considered a serious contender since it was ostensibly Eastern Europe's turn to provide the new secretary general.

However, the Security Council appears to have paid little attention to this informal arrangement, and neither did it heed calls that the top job should be entrusted to a woman this time.