Published: Apr 08, 2010 11:58 AM EDT

PRAGUE (AP) - President Barack Obama says a new arms pact with Russia sets the stage for further cuts in the two nations' nuclear arsenals.

Obama says he and Russian President Dmitry Medvedev (dih-MEE'-tree med-VYEH'-dyev) also have agreed to expand discussions on missile defense, and will aim for a dialogue on cooperation in that area.

The treaty was signed by the two leaders in Prague on Thursday. Obama called the spread of nuclear weapons to more states an unacceptable risk to global security that could raise the specter of arms races from the Middle East to East Asia.

Related: More on the US/Russia Treaty