The United States and Russia on Wednesday concluded the first round of talks aimed at replacing a landmark Cold War-era nuclear disarmament treaty before it expires in December.
Negotiators met behind closed doors to discuss a successor to the Strategic Arms Reduction Treaty (START), in high-stakes talks whose outcome could have far-reaching implications for global security.
A Russian foreign ministry source said that the initial two-day negotiating session had been "successful" and "constructive" and the next round would take place in Geneva next month, news agencies reported.
"The talks have ended. We evaluate them as successful.... The meeting was conducted in a constructive tone," the source was quoted as saying by the Interfax news agency.
Both Interfax and RIA-Novosti reported that negotiators had agreed to meet again in Geneva on June 1-3, but no other details were given about the talks which had begun one day earlier in Moscow.
The Russian foreign ministry said earlier that both sides had agreed to stay quiet about the talks, which are expected to be difficult as negotiators seek to reach a deal before START expires on December 5.
The effort to replace the 1991 treaty is a central element of US President Barack Obama's plan to "reset" badly strained ties with Russia.
Productive negotiations could boost Obama's vision of a world free of atomic weapons and help set the stage for a summit in July when Obama travels to Moscow to meet Russian President Dmitry Medvedev.
Reflecting the difficulties facing negotiators, however, Russian Foreign Minister Sergei Lavrov said on Wednesday that the final treaty needed to take missile defence into account.
His comments appeared aimed at US plans to install elements of a global missile shield in eastern Europe which have angered Moscow and threaten to undermine the START negotiations.
"The general principle of the treaty should be the equal security of both sides and the preservation of parity in the sphere of strategic stability," Lavrov told reporters in Moscow.
"This cannot be guaranteed without taking into account the situation in the sphere of missile defence or the deployment of weapons systems in space, as well as plans to create non-nuclear warheads," he added.
Moscow has consistently demanded that a final agreement must encompass the missile defence issue, include a ban on weapons in space and place limits on strategic missiles armed with conventional warheads.
Washington has resisted including these issues on the agenda for the START talks. The United States also says the missile shield is no threat to Russia and is instead meant to protect against Iran.
Talks on finding a successor to START made little progress under Obama's predecessor, former US president George W. Bush, and many stumbling blocks remain despite a warming of ties under Obama.
Some policy experts have been sceptical that a replacement can be agreed before the treaty expires on December 5.
"The biggest problem on the path to bettering US-Russian relations is the colossal level of political mistrust," said Nikolai Zlobin, the head of the Russia and Eurasia Project at the World Security Institute in Washington.
"Even if it is possible to someday overcome this mistrust, it won't happen soon," he wrote in the Russian state newspaper Rossiiskaya Gazeta.
START, which is seen as a cornerstone of strategic arms control, led to deep cuts in the US and Russian nuclear arsenals after its signing in 1991.
The US negotiating team in Moscow is led by Assistant Secretary of State Rose Gottemoeller while the Russian team is headed by Anatoly Antonov, head of the foreign ministry department for security and disarmament.
