"It is a critical alliance for the United States," the State Department Spokesman John Kirby said.
"There are lots of relevant issues for NATO to consider and to contribute to and, frankly, to lead in," he said, adding that the US is very committed to its role in NATO.
"I don't see that changing," he said, responding to Republican presidential front runner Trump's statement a day earlier that the US needs to rethink its involvement in NATO.
"But we also value the individual skills and capabilities that so many armed forces belonging to NATO bring to the mission," Kirby said in response to a question.
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Meanwhile, Clinton also strongly backed NATO, underlining its importance in the wake of yesterday's terror attacks in Brussels, incidentally, also the headquarters of NATO.
Trump has argued that NATO is a big financial strain on the US and that its allies are not chipping in as much.
Responding to Trump's criticism, Clinton said: "I think it would be a grave error to walk away from Europe, to walk away from NATO, to turn our backs on countries with whom we have a long history and shared values, and frankly, who we need to be working closely with as we defeat ISIS and other terrorist threats. I think NATO has a role to play," Clinton said.
Advocating a light footprint in the world, Trump has said that the US involvement in NATO may need to be significantly diminished in the coming years.
"We certainly can't afford to do this anymore. NATO is costing us a fortune, and yes, we are protecting Europe with NATO, but we are spending a lot of money," he has said.