Russian President Vladimir Putin on Sunday activated Russia’s special deterrence forces, which includes nuclear weapons.

“Top officials in NATO’s leading countries have been making aggressive statements against our country. For this reason, I give orders to the defense minister and chief of the General Staff to introduce a special combat service regime in the Russian army’s deference forces,” Putin said during a televised meeting with his top military aides on Sunday, as reported by Russia’s state-run TASS.

The move puts Russia’s nuclear weapons network on heightened alert, moving it into a ready state that is one step away from a launch.

Russian analyst Pavel Podvig told The Wall Street Journal that Putin’s move “is not necessarily preparation for a strike” but “prepares it to act quickly if needed.”

Putin insisted that his decision was in reaction to harsh actions against Russia, including “illegitimate sanctions” that the U.S. and NATO nations enacted in recent days.