The State Department said Friday that Clinton would visit London, Dublin, Belfast and Moscow from Oct. 9-15. The journey marks her first solo trip as America's top diplomat to Britain and her first to Russia.
It comes after diplomats from those countries, the United States, China, France and Germany met this week with Iran's chief nuclear negotiator over its suspect atomic program.
State Department spokesman Ian Kelly said that while in Belfast, Clinton would reaffirm "unwavering U.S. support" for the Northern Ireland peace process. In Moscow, she will be discussing progress on negotiating a successor to the 1991 Strategic Arms Reduction Treaty, or START I, before it expires on Dec. 5.
Agreement on that is crucial for the U.S. and Russia to keep an eye on one another's nuclear stockpiles and add credibility to their efforts to persuade countries such as Iran and North Korea to abandon their nuclear programs.