"Russia now has a last chance. If Russia does not come back into compliance, well, then we have a big problem because then the INF Treaty is breaking down," Stoltenberg told Germany’s dpa news agency.
US President Donald Trump said in October he wanted to pull the country from the deal but was persuaded by European allies in December to give Russia a 60-day grace period until mid-February to comply.
Russia has rejected the accusations. It has complained about US weapons in Europe that can fire cruise missiles at ranges that are in breach of the INF. Russian Foreign Minister Sergey Lavrov has accused the United States of refusing to address mutual concerns together.