Russia has vowed it won't fire any new missiles — as long as the U.S. promises to do the same.
On Sunday, Russian Defense Minister Sergey Shoygu said: "We will stick to that. Unless there are such systems in Europe."
The U.S. left the Intermediate-Range Nuclear Forces treaty, or INF treaty, on Aug. 2, because NATO found Russia violated the treaty by launching a new ground-launched cruise missile.
The treaty banned ground-launched ballistic and cruise missiles with ranges between 310 miles and 3,400 miles. Those types of missiles make it easier for strikes with limited notice as they can land within 10 minutes.
Since both countries left the INF treaty, there has been speculation throughout NATO about what this means for the U.S., Russia and Europe.