The new Strategic Arms Reduction Treaty (START) to be signed on April 8 by the two leaders builds on a previous agreement that expired in December.

Obama has called the treaty the "the most comprehensive arms control agreement in nearly two decades" and said it would cut the nuclear weapons of the United States and Russia by about a third.

After meeting with Medvedev and attending the signing ceremony in Prague, the Czech Republic capital, Obama will have dinner with heads of government from 11 countries -- Bulgaria, Croatia, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania, Slovakia and Slovenia.

The highlight of the two-day trip is the new treaty with Russia, which is another step in nuclear arms relations between the former Cold War adversaries. Its signing comes two days after the Obama administration announced a new U.S. nuclear weapons policy and four days before Obama convenes a summit of 47 nations on nuclear security issues.