Flags of NATO members fly outside the NATO headquarters in Brussels, Tuesday, Jan. 10, 2023 (AP Photo/Olivier Matthys)

A European official told the Foreign Policy journal on Monday that the selection method for a new NATO Secretary General is very ambiguous, with the bloc's top members wielding undue influence over the process.

"It is the least transparent election of all elections," the anonymous diplomat was quoted saying by FP.

According to the source, Dutch Prime Minister Mark Rutte, Canadian Deputy Prime Minister Chrystia Freeland, and Estonian Prime Minister Kaja Kallas are among the likely nominees to succeed Stoltenberg as NATO secretary general.

Stoltenberg's term as Secretary General was set to finish in October 2022, but it was extended for another year, until September 30, 2023, owing to the Ukraine crisis.

Last year, The New York Times identified Slovak President Zuzana Caputova and former Croatian President Kolinda Grabar-Kitarovic as strong candidates to succeed Stoltenberg.

On Sunday, a NATO alliance spokesperson reported that Stoltenberg has no plans to extend his mandate.

Welt am Sonntag, a German newspaper, reported that a number of NATO member states preferred if Stoltenberg remained in his position while the war in Ukraine continued.