On Monday, the Russian government announced that it had successfully tested a short-range interceptor missile, nicknamed “Satan,” as part of its ongoing effort to develop a domestic missile defense system, reports Russia’s RIA News Agency.

Russia also is working on the development of a 100-ton ballistic missile, Pravda reports.Russia’s opposition to American missile defense plans in Eastern Europe seems to be at the center of these proceedings, explains Yahoo! News.

“In connection with the plans of the United States to develop the air defense system in Europe, in close vicinity to Russia’s borders, and because of the unwillingness of the U.S. side to provide any guarantees, the Russian Federation continues to take measures to preserve parity in the field,” says Pravda.

“The United States is unwilling to provide a written guarantee that the system would not be used against Russian nuclear forces,” the Union of Concerned Scientists’ Elliot Negin wrote at Huffington Post Monday. “[Dmitry Medvedev] warned that, if the United States carries out its plans to build it without such an assurance, Russia would site missiles in its westernmost Kaliningrad region and consider walking away from the New START agreement.”

“Russia’s military establishment is concerned about losing parity with the United States on the number of deployed strategic nuclear warheads that it maintains,” the Ploughshare Fund’s Joel Rubin also told Yahoo! News. “By developing a new heavy missile, a perverse outcome is taking place, where Russia is attempting to not fall further beneath New START levels in order to satisfy the concerns of its military establishment.”