"He has, in meetings with me and publicly when I met him in the White House last month, stated that he's committed to NATO," Stoltenberg said on CBS' "Face the Nation." "His security team has also stated that very clearly."
During his presidential campaign, Trump called NATO "obsolete." But after meeting with Stoltenberg in April, Trump said he'd changed his views
after NATO's leaders assured him the group would turn its attention to combating terror groups such as ISIS.
Stoltenberg pointed to the US moving to ramp up its military presence in Europe as proof of Trump's new position.
"More important is that the US is now increasing their military presence in Europe for the first time since the end of the Cold War," Stoltenberg said. "President Trump just suggested a 40% increase in funding for US military presence in Europe. We will have a new armored brigade. We will have more training, more equipment, more infrastructure. So actions speak louder than words."
Stoltenberg told CNN in an interview later Sunday that NATO could do more to counter threats from groups like ISIS.
"I agree with President Trump that NATO can do much more."
At the summit in May, NATO officially joined the coalition against ISIS. All NATO members had already individually joined the coalition
"We will sit down with all the members of the coalition and discuss what more we can do," Stoltenberg said.
Stoltenberg said people shouldn't read much into Trump declining to pledge he would uphold NATO's Article 5
at the summit. Article 5 requires NATO members to come to the defense of an ally who is attacked.
Stoltenberg said Trump's stated commitment to NATO implied that he would stand by Article 5.
Nikki Haley, the US ambassador to the UN, said on CNN's "State of the Union" Sunday that "of course" the US believes in Article 5.
"We never swayed from Article 5," Haley said. "I think if you asked him (Trump) if he was in favor of Article 5, he would say yes."
At that summit, Trump hammered NATO members
for not spending 2% or more of their GDP on defense. Stoltenberg said Trump's constant refrain on defense contributions had helped convey the message to member nations.
He said he anticipated more allies would reach the 2% target in the next year or two.