Washington ( CNN ) -- The United States and Russia say they will be unable to reach a deal on an arms control treaty by the end of the year to replace their existing one , which expired this month . Assistant Secretary of State P.J . Crowley told reporters Tuesday that the U.S. delegation -- led by Assistant Secretary Rose Gottemoeller -- had returned for a recess from the START negotiations in Geneva . Talks are expected to resume in mid-January with new proposals . `` The team has gone through an intensive period of negotiations with their Russian counterparts over more than two months , '' Crowley said . `` Our goal remains to conclude a solid treaty for the president 's signature as soon as possible . '' The 1991 Strategic Arms Reduction Treaty , commonly known as START , expired on December 5 but the leaders agreed to honor its spirit until a new treaty could be negotiated to replace it . President Obama and Russian President Dmitry Medvedev , who met last week in Copenhagen , Denmark , had hoped to sign an agreement by the end of the year . A statement on the Russian Foreign Ministry 's Web site said , `` Preparation of the new treaty is practically complete '' but `` a few problems have to be overcome in order to finalize the treaty and submit it to [ the ] presidents of Russia and the United States . This will be done very soon . '' `` Having resolved most issues discussed in recent months , delegations arrived at corresponding positions , '' the statement said . `` The Russian side would like to emphasize the talks have been constructive and business-like . It reflects partnership and mutual respect which characterize the current stage in the relations between Russia and the United States . '' Crowley also cited a few `` hurdles '' to an agreement , including the complexity of the weapons systems , agreement on the numbers of warhead reductions , and verification . But he said the two sides hope to finalize a deal to replace START when they meet next month . `` Clearly , over the course of these two months , we have made dramatic progress , '' he said . `` There are still issues that we continue to work through , so there 's still more work to be done . But I think we remain confident that , given good faith and the ongoing efforts of both sides , that this will get done . ''
Talks are expected to resume in mid - January with new proposals . The Strategic Arms Control Treaty expired on December 5 . Russia agreed to honor START until a new treaty could be negotiated . American and Russian presidents had hoped a new agreement could be ready this year .