Blinken was due to brief his NATO counterparts on the U.S. intelligence picture on the group's eastern flank and in Ukraine, which is not a member.
At a news conference in Latvia before the meeting, Blinken expressed alarm at the "unusual" Russian troop movements.
Two Russian troop build-ups this year on Ukraine's borders have alarmed the West. In May, Russian troops there numbered 100,000, the largest since Russia's annexation of Crimea in 2014, Western officials say.
Moscow has dismissed as inflammatory Ukraine's suggestions that it is preparing for an attack, said it does not threaten anyone, and defended its right to deploy troops as it wishes.