GENEVA (AFP) - Russia and the United States on Monday began a a second round of talks on renewing a key Cold war-era nuclear arms reduction treaty in a positive atmosphere, a diplomat said in Geneva. A member of the Russian delegation told AFP after the first day of the meeting on the Strategic Arms Reduction Treaty (START), which expires on December 5, that the negotiations were positive and business-like. A US spokesman declined to comment on the talks behind closed doors at the Russian mission in the western Swiss city of Geneva. The negotiations move to the US mission on Tuesday and might not continue for a scheduled third day if the negotiators from Washington and Moscow manage to complete their agenda early, a Russian diplomat said. Officials from both sides expect to reveal few details on the substance of their talks, which set the scene for a US-Russian summit on July 6 to 8. First results from the START negotiations, which began in Moscow two weeks ago, are due to be unveiled by Obama and Dmitry Medvedev when they meet in the Russian capital, a Russian diplomat said. US State Department spokesman Ian Kelly said: On the details of the negotiation, I think we prefer to keep that in private right now. START, signed in 1991 just before the break-up of the Soviet Union, which bound both sides to deep cuts in their nuclear arsenals, is due to expire on December 5. The agreement this year to seek its renewal marked the first tangible step in the thaw in US-Russian relations heralded by the Obama administration.