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NATO Secretary-General Jens Stoltenberg says the alliance is studying options to deal with what it insists are Russian violations of a key missile treaty but that it wants to avoid sparking any arms race.

Speaking at NATO headquarters Wednesday, where defense ministers are discussing the future of the imperiled Intermediate-Range Nuclear Forces (INF) treaty, Stoltenberg said: "This is very serious. We will take our time."

On Feb. 2, Washington launched the six-month process for leaving the INF, insisting that a new Russia missile system breaks the pact's range requirements. Russia denies violating the 1987 treaty and says it is pulling out, too.

Stoltenberg says NATO has many options but that its response "will be measured and it will be defensive because we don't want a new arms race."