Russia's military on Friday warned the US that it would not reduce its nuclear arsenal until Washington made clear whether or not it would go ahead with a controversial missile shield in Central Europe.

The comments by the country's top general exposed a potential hitch as the two sides hold talks on replacing a key Cold War-era nuclear arms reduction treaty by the end of the year.

"While the situation in the world is unclear, including concerning the missile defence system, we will not touch our nuclear potential," Russian news agencies quoted the army's chief of staff Nikolai Makarov as saying.

Makarov was referring to the US plan to install missile defence facilities in the Czech Republic and Poland, which Moscow insists is a threat to its security even though Washington says it is directed against Iran.

The plan was initiated by the previous US administration of George W. Bush but President Barack Obama has pledged to press ahead with the missile shield but indicated he could drop the project if Iran is no longer deemed a nuclear threat.

"We will be making practically no changes to the Russian strategic missile forces," added Makarov.

"Strategic nuclear forces are a sacred question for us and we will give them as many resources as required to preserve stability in the world and keep it at an appropriate level," he added.

The announcement from Makarov comes as Russia and the United States hold talks aimed at cutting their nuclear arsenals and finding a successor a 1991 treaty due to expire at the end of the year.

The Interfax news agency quoted a source in the Russian foreign ministry as saying the latest talks on replacing the treaty had been "constructive".

The confidential negotiations are meant to feed in to a summit between Obama and his Russian counterpart Dmitry Medvedev in Moscow on July 6-8 that is expected to push forward improving ties.

The 1991 Strategic Arms Reduction Treaty (START), signed just before the break-up of the Soviet Union, commits both sides to deep cuts in their nuclear arsenals. It expires on December 5.

The United States and Russia also have the more recent Strategic Offensive Reductions Treaty signed in 2002, which went further than START with lower caps on the total deployment of warheads.

Russian President Dmitry Medvedev said Friday that "unchecked proliferation of nuclear weapons threatens all mankind" and that both Russia and the United States were aware of their responsibility to other nations as nuclear powers.

A senior Russian diplomat said this week that Moscow was still awaiting a "concretisation" of signals from the US on the missile shield, which he said Russia still deemed "an unnecessary complication in bilateral relations."

Ties between Russia and the United States plunged to a post-Cold War low in the last months of the Bush presidency after Moscow's war with Georgia but the tone has improved drastically since Obama came to power.

Makarov also complained that the Georgian armed forces were now better equipped with weapons and military hardware than they were in the August war.

He added that Russia would also carry out large-scale military exercises in its neighbour Belarus in September.