The head of NATO on Monday praised embattled US Secretary of State Rex Tillerson for his "key role" in the North Korea crisis as rumours swirl that his position is under threat.

Jens Stoltenberg insisted that a meeting of NATO foreign ministers in Brussels this week would not be distracted by doubts over Tillerson's future.

Anonymous White House leaks have suggested Tillerson could be out of a job within weeks and even while denying this on Friday, President Donald Trump reminded him: "I call the final shots."

Stoltenberg gave his backing to Tillerson's efforts in tackling the crisis surrounding Pyongyang's nuclear and ballistic missile tests.

"Secretary Tillerson has played a key role, both in sending the message of deterrence, the unity and the resolve of the whole alliance, but also when it comes to the need for continuing to work for a peaceful solution," Stoltenberg told reporters in Brussels.

Trump has publicly criticised his top diplomat on the issue, saying Tillerson was "wasting his time" pursuing contacts with North Korea.

Tillerson has dismissed reports that Trump aides want him to resign as "laughable", but rumours are set to dog his diplomatic tour of Europe, which also includes visits to Paris and Vienna.

North Korea will be high on the agenda at the NATO meeting after Pyongyang last week tested its most powerful intercontinental ballistic missile, which it says brings the whole of the continental United States within range.

- 'No change whatsoever' -

Questions have been raised about whether the reported rift with Trump undermines Tillerson's ability to negotiate with allies, but Stoltenberg said he had no concerns.

"We have seen again and again that NATO and NATO ministers are able to focus on the core task, on the job we have to do, despite any speculations and rumours, and I am absolutely certain that this will be the case also now," Stoltenberg said.

"I am absolutely certain that all ministers -- including secretary Tillerson -- will focus on that task and be able to make important decisions."

Rumours about Trump and Tillerson's fractious relationship came to a head on Thursday when several US media outlets -- citing White House sources -- predicted Tillerson's resignation and replacement by CIA chief Mike Pompeo.

Trump rejected the reports as "FAKE NEWS" in a tweet, but acknowledged the pair had policy differences.

The US Ambassador to NATO, Kay Baley Hutchison, also insisted Tillerson still spoke for the president.

"We have been working with Secretary Tillerson and his staff on this meeting for several weeks and there has been no change whatsoever," she told reporters in Brussels on Monday.

The North has staged six increasingly powerful atomic tests since 2006 -- most recently in September -- which have rattled Washington and its key regional allies South Korea and Japan.

Source:AFP