Norway's foreign minister said on Sunday he regretted that criticism of the United Nations secretary-general by Oslo's ambassador had been leaked days before a visit from the UN chief.

Ambassador Mona Juul accused Secretary-General Ban Ki-moon of weak, ineffective and at times counterproductive leadership, the daily Aftenposten had reported on Wednesday.

The newspaper published what it said was a letter from Juul to the foreign ministry in which she said Ban was late in handling challenges and his abrasive style irked diplomats.

"I regret that it happened, but let me stress that this is a report to the Norwegian Foreign Ministry, it was not a statement by the Norwegian government," Foreign Minister Jonas Gahr Stoere told reporters.

Stoere said Norway continued to be a strong supporter of the United Nations and its South Korean chief.

"This is not the time to waste resources on commenting on job performance, this is a time of renewing our support to the UN and thereby the support to the current Secretary-General, whom I have experienced as very hard-working and dedicated," Stoere said.

He said Ban was "heartily welcome" to Norway in one week, for talks with Prime Minister Jens Stoltenberg and himself in Oslo and a visit to Arctic archipelago Svalbard. – Reuters