The United States and Russia have failed to clinch a new nuclear arms control treaty this year, denying the White House a quick boost in its efforts to demonstrate improved relations with Moscow.

The two sides hope to reach a deal in early 2010, the U.S. said Wednesday.

The American delegation led by Assistant Secretary of State Rose Gottemoeller has left for the United States and will return to Geneva for more negotiations in January, the U.S. diplomatic mission in Geneva said.

"Our goal remains to conclude a solid treaty for the presidents'' signature as soon as possible," it said.

Presidents Barack Obama and Dmitry Medvedev had been hoping to sign a new deal before the end of the year, but conceded last week at climate talks in Copenhagen that their goal was unlikely to be met.

The 1991 Strategic Arms Reduction Treaty expired Dec. 5, and both countries have agreed to continue to honor its main provisions until a successor treaty is in place. The START treaty successor is seen as one of the most achievable areas of cooperation. Washington is also seeking help from Moscow on trickier issues such as the standoff over Iran''s uranium enrichment program.