Russia has warned the U.S. and its allies against allowing Ukraine to join NATO. This morning, a member of Russia’s Security Council told Russian state media, “Kyiv is well aware that such a step would mean a guaranteed escalation to a World War III.” The comments came as officials from 50 countries, including all 30 NATO members, met in Brussels, where they pledged to step up arms shipments to Ukraine, including new air defense systems. Following the talks, U.S. Defense Secretary Lloyd Austin was asked about Russia’s threats to use nuclear weapons.

Secretary of Defense Lloyd Austin: “Putin’s saber-rattling is reckless — nuclear saber-rattling is reckless and irresponsible. We don’t expect to see and hear that kind of behavior from a major nuclear power, and so that’s very dangerous. And you’ve heard a number of leaders around the world emphasize that.”

Austin’s comments come just days after Poland’s president said he’s open to stationing nuclear weapons on Polish soil and has discussed the idea with the United States.