The United States and Russia have been seeking to thrash out a successor to the 1991 Strategic Arms Reduction Treaty (START), seen as a cornerstone of strategic arms control, before it expires in December.

US President Barack Obama and his Russian counterpart Dmitry Medvedev are expected to reveal what progress has been made when Obama visits Moscow in early July, said Russian foreign ministry spokesman, Andrei Nesterenko.

"The talks are proceeding in a constructive and businesslike tone. We are working from the assumption that at the July summit the presidents will be able to announce the interim results," Nesterenko told reporters in Moscow.

He added that the third round of START talks would take place June 23-24 in Geneva, after the first round was held May 19-20 in Moscow and the second round was held June 1-3 in Geneva.

START, which led to deep reductions in the US and Russian nuclear arsenals, expires on December 5 and talks on finding a successor agreement made little progress under the administration of former US president George W. Bush.

Relations between Washington and Moscow have warmed somewhat under Obama and the two sides have pledged to push hard for a new treaty, but obstacles remain, notably on the issue of the planned US missile shield that Russia opposes.