Meanwhile, Stoltenberg made it clear that NATO will "take the necessary steps to provide credible and effective deterrence" against Russia.
During his speech, Stoltenberg also called for unity in the bloc while recognizing serious divergence. "Questions are being asked on both sides of the Atlantic about the strength of our partnership. And, yes, there are differences," he said.
U.S. President Donald Trump has long been blaming the NATO countries that they have not met the 2-percent benchmark on military spending.
NATO is holding two-day foreign ministers' talks to commemorate its establishment for seven decades. Russia is set to be a major issue for the discussion.
The INF Treaty, signed in 1987 between the Soviet Union and the United States, marked the first-ever pact reached by Washington and Moscow on nuclear disarmament and a major step forward in restricting the arms race.
However, the two sides have been accusing each other of violating the arms control agreement amid increasing tensions in recent years. Moscow announced in early March about its suspension of complying with the pact, following a similar decision by Washington in February.