Talks between Russia and the United States on a new nuclear disarmament treaty must overcome serious difficulties but should result in an agreement early next year, Russia's top general said Monday.

"We will reach a new agreement at the beginning of next year. But there are some serious difficulties," the chief of Russia's armed forces general staff, Nikolai Makarov, said in a speech in Moscow.

The Russian foreign ministry said earlier that negotiations in Geneva on a new treaty will resume in January after officials returned to their capitals for the new year without reaching an agreement.

The Strategic Arms Reduction Treaty (START), signed in 1991 just before the breakup of the Soviet Union, set limits and a system of mutual inspections on each sides' nuclear arsenals but expired on December 5.

Makorov told AFP after the speech that the difficulties include agreeing limits on the number of delivery vehicle "carriers" and nuclear warheads as well as the telemetry of the missiles, among other issues.

But he added: "We got so close that it allows us to say with confidence that we will conclude such an agreement in January."

US President Barack Obama and Russian President Dmitry Medvedev declared on the sidelines of the UN climate talks in Denmark last week that the sides were on verge of concluding a deal.

But Medvedev also admitted that technical details needed to be worked out.

Medvedev and Obama set a goal for the replacement treaty in July of slashing the number of warheads on either side to between 1,500 and 1,675 and the number of "carriers" capable of delivering them to between 500 and 1,100.

The United States has said it currently has some 2,200 nuclear warheads, while Russia is believed to have about 3,000.