Chicago is the site of Group of Eight and NATO summits next spring. Russian Deputy Foreign Minister Sergei Ryabkov said Moscow might skip the NATO summit unless it secures agreements over European missile defense.
"If we agree on the missile defense issue, it would be much easier for us to make a positive decision about the summit," he was quoted by Russian state-run news agency RIA Novosti as saying. "We do not know whether or not we will agree."
Last month, Russian President Dmitry Medvedev said Moscow would respond in kind should the United States place a missile shield near his country.
U.S. Secretary of State Hillary Clinton stressed that a European missile defense system wouldn't upset the strategic balance with Russia. Its intent, she maintained, is to deter Iran.
Moscow in August 2010 deployed its S-300 missile shield to Georgia's breakaway republic of Abkhazia to protect the airspace from "intruders."
Medvedev had said the 2008 war with the former Soviet republic of Georgia stopped NATO's expansion eastward and Moscow this week threatened a repeat should Tbilisi move closer to the Western alliance.
Notable deaths of 2014 [PHOTOS]