NATO Secretary General Jens Stoltenberg is set to extend his term as head of the alliance by another year due to the war in Ukraine, Norwegian broadcaster TV2 and daily Dagens Naeringsliv reported on Thursday, citing unnamed sources.

Stoltenberg's term expires on Oct 1 and he had been due to take up a post as central bank governor of his native Norway by the end of 2022.

Asked as he arrived at a NATO summit in Brussels on Thursday whether he would stay on at NATO, Stoltenberg said: "I will leave that decision to the 30 leaders to decide."

Russia's invasion of Ukraine a month ago, which Moscow calls a "special operation", has triggered Europe's largest refugee crisis since World War Two and led Western nations to fundamentally rethink their defence policies.

Stoltenberg, an economist by training and former leader of Norway's Labour Party, was Norwegian prime minister from 2000-01 and 2005-13 before becoming NATO chief the following year. He has also been finance minister and energy minister.

The Norwegian government last month named deputy central bank chief Ida Wolden Bache governor of Norges Bank for up to nine months, with Stoltenberg slated to take the top job by year-end.

The central bank governor is in charge of setting interest rates and managing financial stability as well as overseeing Norway's sovereign wealth fund, the world's largest with assets of $1.4 trillion.