Washington (CNN) The head of NATO expressed optimism regarding the future of the alliance's relationship with the US Wednesday, despite the election of a US president who has expressed skepticism about the alliance.

"The US commitment to NATO and the US commitment to the collective defense of Europe has been rock-solid for almost 70 years and I'm absolutely confident that, that will still be the case," NATO Secretary General Jens Stoltenberg said, adding, "I'm confident because a strong NATO is important for Europe, but it's also of great importance for the United States."

Stoltenberg's optimistic assessment seemed to provide a preview of areas where he thinks NATO can collaborate with the newly minted President-elect while also indirectly pushing back on other issues of potential disagreement.

Trump made a habit of questioning NATO's relevance while on the campaign trail, a departure from over 60 years of bipartisan foreign policy.

What Trump says about NATO and what it actually does

What Trump says about NATO and what it actually does 02:23

What Trump says about NATO and what it actually does

Trump's biggest criticism of the alliance has been that its members do not meet the recommended domestic defense spending level of 2% of GDP.

"The 28 countries of NATO, many of them aren't paying their fair share," Trump said during the September debate. "That bothers me."

Currently, only five allies meet the 2% threshold. NATO officials have long-called on the member states to boost their defense budgets, while also noting that NATO's European states have increased spending and that several countries plan to hit that target in the coming years.

Stoltenberg agreed Wednesday that the issue of defense spending was "fair to raise," though he noted that European countries are now "stepping up and spending more on defense."

Trump has also hammered away at NATO because "they do not focus on terror."

He said at September's presidential debate, "I think we have to get NATO to go into the Middle East with us."

Stoltenberg was quick to push back on this notion Wednesday, saying NATO plays "a key role in the fight against international terrorism."

He noted the only time NATO invoked its collective defense clause was after the terrorist attacks on September 11 and pointed to the NATO operation in Afghanistan, which he called the alliance's biggest, and the recent deployment of NATO's surveillance aircraft to aid the fight against ISIS.

"We are in Afghanistan to fight terrorism to prevent Afghanistan becoming a safe haven for international terrorists," Stoltenberg said.

And NATO announced Wednesday a new naval mission aimed at patrolling the Mediterranean Sea, with counter-terrorism of the core tasks.

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At the same time, in recent weeks, Trump has also struck a more conciliatory tone towards the 28-member defense alliance at points, saying "I'm all for NATO," during September's debate.

Stoltenberg alluded to the President-elect's recent praise of the alliance while speaking to CNN's Christiane Amanpour, saying, "Donald Trump has clearly stated that he is a big fan of NATO and that has been the case for all American Presidents."

But Stoltenberg's reference to the "rock-solid" American commitment to collective defense appeared to push back on comments made by Trump in July, where he seemed to imply that the US should not come to the aid of a NATO member that's attack if the country is not meeting its commitments.

Trump was criticized by members of his own party for the comments.

But Newt Gingrich, a Trump ally whose could play a role in the Trump administration, went even further.

The former speaker of the US House cast doubt on whether Washington should defend some of NATO's eastern members, like Estonia, from Russia.

"I'm not sure I would risk a nuclear war over some place which is the suburbs of St. Petersburg," Gingrich told CBS' "This Morning" in July.

Perhaps as part of a bid to clear the air, within hours of Trump's victory, Stoltenberg said he looked forward to meeting Trump, welcoming him to Brussels for next year's NATO summit and to discussing "the way forward."

But what is not clear is what such conversations will look like given Trump's past criticisms of the bloc.

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NATO has also made efforts to bolster its presence in Eastern Europe as part of an effort to deter Russia after Russian troops annexed Crimea in 2014.

While these deployments, including a battalion of US troops to Poland, have been welcomed by the host nations, they have irked the Kremlin and Trump has made improved relations with Moscow a central theme of his foreign policy approach.

On the other hand, Trump has praised some of NATO's more recent moves in bolstering its intelligence-sharing efforts, including the establishment of a new post, assistant secretary general for intelligence and security.

"I think that's great," Trump said of the new post, saying that his criticism of the alliance helped drive its creation.

NATO officials have long said the establishment of the new position was not tied to the US presidential campaign.

Perhaps providing insight into Trump's thinking on NATO, Nigel Farage, one of the leaders of the UK drive to leave the EU who has appeared alongside Trump at rallies, told Britain's Express that while Trump was right to call on allies to boost defense expenditures, he backed the US staying in the alliance.