Washington and its allies say a missile defense shield in Europe would counter regional aggression for adversaries such as Iran. Russia, however, said it viewed the plans as a threat to its national security, warning it may take corresponding action along its western border.
NATO Secretary-General Anders Fogh Rasmussen told Radio Free Europe/Radio Liberty that bilateral agreements reached in Portugal in 2010 outlined a strategic partnership between NATO and Russia.
"Threats to deploy offensive weapons directed against NATO territory ... are not in accordance with the development of a true strategic partnership," he said.
U.S. Deputy Assistant Secretary of Defense James Townsend told U.S. lawmakers last week that European missile defense was vital to addressing regional threats to the NATO alliance given the state of the European economy.
"In Chicago, we expect to further that goal by taking steps to advance the implementation of our missile defense system," he testified.
Chicago is the site of a NATO summit this week.