President Barack Obama's top military adviser attended the latest talks with Russia to replace an expiring Cold War-era arms control agreement, the U.S. said Tuesday.

Adm. Mike Mullen, Chairman of the Joint Chiefs of Staff, met with Russian officials from Sunday to Tuesday, U.S. spokesman in Geneva Michael Parmly said.

Obama and Russian President Dmitry Medvedev want to conclude a new treaty by Dec. 5, when the 1991 START I accord cutting U.S. and Russian nuclear arsenals expires.

Mullen met Tuesday in Geneva with Russian armed forces chief of staff Gen. Nikolai Makarov, and the two discussed "military and technical issues" related to START, a spokesman for Mullen said.

"Both sides noted that the discussions were both candid and productive and that negotiations were proceeding in a positive direction," the spokesman, Capt. John Kirby, said in a statement.

Russian Foreign Ministry spokesman Andrei Nesterenko said Tuesday that the talks on a replacement for START were in the "home stretch," but he stressed "they are not over."

He said both sides were intensely focused on substantive issues and on "the search for mutually acceptable compromises" as they try to reach agreement.

U.S. officials have said there is the broad outline of an agreement, but talks are ongoing on how to verify new cuts in nuclear arsenals.