NATO chief Jens Stoltenberg on Friday voiced confidence that Donald Trump was committed to the transatlantic alliance, which has stood the test of time for both the United States and Europe.

"I am absolutely confident President-elect Trump will maintain America's strong commitment to European security and to NATO," Stoltenberg told AFP in an interview in Brussels.

"That is in the interests of both Europe and the United States," he said, with the disasters of two World Wars and the Cold War showing how inter-connected both sides' security was.

The only time NATO's Article 5 "all for one, one for all," collective defence guarantee had been invoked was after the 9/11 terror attacks on the United States, he recalled.

Stoltenberg said he expected Trump to continue to press NATO allies to increase defence spending, just as previous US presidents had, and this was fully justified.

Washington accounts for nearly 70 percent of the NATO allies combined defence outlays and has long demanded they do more.

Trump caused consternation on the campaign trail when he suggested Washington might think twice about coming to the defence of an ally if it had not paid its NATO dues.

NATO announced later Friday that Stoltenberg had had a "good talk" with Trump on the alliance's future.

He had thanked him in particular for raising the issue of defence spending, a "top priority" for the secretary general since he took office in 2014, it said in a statement.

"The two leaders agreed that progress has been made on fairer burden-sharing but that there is more to do," it added.

- 'Russia cannot be isolated' -

Trump's more positive approach to President Vladimir Putin also rattled allies who at a July Warsaw summit had endorsed NATO's biggest military build-up since the end of the Cold War to counter a more assertive Russia.

Stoltenberg said he did not see an issue.

"What I have heard is that he has conveyed a message about also talking to the Russians. At our Warsaw summit, we made decisions on strong defence but also on political dialogue" with Moscow, he said.

"Russia is our biggest neighbour, Russia is here to stay; there is no way we can isolate Russia so we have to continue to strive for a more constructive relationship with Russia."

Pundits in Europe largely took Trump's campaign comments at face value, wondering if the new president was about to ditch Washington's 70-year security guarantee for Europe in favour of a more isolationist, "America First," policy.

Since his stunning upset election victory, opinion has veered sharply, with some believing the demands of office will prove a reality wake-up call while others argue Trump meant what he said.

- Turkey a 'key ally' -

Stoltenberg also confirmed that several Turkish officers posted to NATO commands had sought asylum after a bloody failed coup in July sparked a massive crackdown and purge.

NATO and its European allies have stressed Ankara has the right to prosecute the coup plotters but say it must do so while respecting the shared democratic values the alliance is meant to uphold.

Turkish President President Recep Tayyip Erdogan has chafed at the criticism, saying the allies do not fully appreciate the threat posed by the coup.

"Turkey is a key ally, is a highly valued ally ... and plays an important role in the alliance not least because of its strategic location," Stoltenberg said.

He said he had visited Turkey shortly after the coup and seen the damage inflicted on the parliament building by F16 fighter jets in an assault on democracy.

The Turkish authorities have the right to track down those responsible but "it is important that this is done ... in accordance with the rule of law," he said.

Stoltenberg said he was going back to Turkey on Sunday to attend a meeting of the NATO parliamentary assembly which brings together member state MPs.

"I expect an open debate," he said.