Speaking on his first visit to NATO headquarters, Blinken said the alliance was at a pivotal moment in facing threats around the world, as well as with climate change.
NATO Secretary-General Jens Stoltenberg has set out areas where NATO could modernize over the medium term - from climate measures to more sustainable funding of military operations - and needs U.S. support.
Asked about any possible withdrawal from Afghanistan, Blinken said that Washington would not act unilaterally.
"We went in together. We have adjusted together. And when the time is right, we will leave together," he said.