Russia and the United States were set to pursue talks on a key nuclear arms reduction treaty for a third day, diplomats said Tuesday, as Moscow suggested that an initial deal could be ready by next month.

Russian and US negotiators "ended their discussions for today and will continue tomorrow (Wednesday) at the Russian mission," a Russian diplomat told AFP on condition of anonymity.

A spokesperson for the US Mission to the United Nations in Geneva said: "The talks will continue tomorrow on June 3 for a half day as planned."

But officials from both sides in Geneva were keeping silent about the state of play in their second round of negotiations on replacing the 1991 Strategic Arms Reduction Treaty (START), which are due to feed into a US-Russian summit on July 6 to 8.

A Kremlin spokeswoman said in Moscow Tuesday that Russia does not rule out reaching initial agreement with the United States on nuclear arms cuts by the time US President Barack Obama meets President Dmitry Medvedev in the Russian capital.

"A complicated process is under way," said Medvedev's spokeswoman, Natalya Timakova.

"I wouldn't say that we won't be able to achieve a more concrete accord," she told journalists in a telephone briefing, adding it was "too early to draw conclusions."

START, signed in 1991 just before the break-up of the Soviet Union, bound both sides to deep cuts in their nuclear arsenals.

The agreement this year to seek its replacement before it expires on December 5 marked the first tangible step in the thaw in US-Russian relations heralded by the Obama administration.

However, on top of the complex technical issues involved in the landmark disarmament treaty, the negotiations are dogged by bargaining over US plans for an missile defence shield partly stationed in Europe, a project which has angered Russia.