NATO has announced the alliance's missile shield is up and running with a basic capability to shoot down incoming missiles.
NATO Secretary General Anders Fogh Rasmussen made the announcement at the NATO summit in Chicago.
If all goes according to plan, NATO will have all of Europe and the United States covered with the missile shield by 2022.
Russia opposes the system, saying it will neutralize its own nuclear deterrent.
Rasmussen repeated Russia has "nothing to fear," and expressed hope Moscow will eventually agree to cooperate on missile defense.
Earlier, Russian Deputy Defense Minister Anatoly Antonov again warned NATO not to go ahead with the plan, arguing it would disrupt the global strategic balance.
Russia has already threatened military retaliation over the plan.
Based on AP, dpa and AFP reporting