U.S. President Barack Obama and his Russian counterpart, Dmitry Medvedev, say their two countries will pursue an arms deal cutting nuclear warheads below levels agreed in 2002.
The agreement emerged after the two presidents met for their first face-to-face talks in London, ahead of the G20 summit.
The proposed arms deal would go beyond the 2002 Strategic Offensive Reductions Treaty (SORT), which committed both sides to cutting arsenals to between 1,700 and 2,200 warheads by 2012.
They said they have ordered negotiators to report first results in July.
In a joint statement, Obama and Medvedev also agreed to work together on Afghanistan, urged Iran to restore confidence in the peaceful nature of its atomic program, and expressed concern about an upcoming North Korean rocket launch.
They also acknowledged lingering differences over last year's Russia-Georgia war and over U.S. proposals to base parts of a missile shield in Eastern Europe, something Moscow considers a threat to its security.
Obama has shown less enthusiasm for the missile-defense proposal than his predecessor George W. Bush, and has indicated to Medvedev that Washington would consider scrapping the idea if Moscow offered assistance in curbing Tehran's nuclear ambitions.
Fyodor Lukyanov, editor of the Moscow-based journal "Russia In Global Affairs," tells RFE/RL's Russian Service that both Medvedev and Obama will likely aim to secure an early breakthrough by initially focusing on issues where there is less disagreement.
"It seems that both sides are taking a pragmatic approach by starting with issues where there can be fast progress," Lukyanov says. "I think there are two such issues. First, there is the Strategic Arms Reduction Treaty, which expires at the end of this year. There is not any disagreement that this treaty needs to be extended. The second issue where there is a possibility for success is Afghanistan, since there are no conflicts between Russia and the United States on this. The prospect of the Taliban returning to power doesn't make either side happy."
'Sizing Each Other Up'
Russia has agreed to allow NATO to transport nonmilitary supplies to Afghanistan via Russia, but relations have been complicated by Kyrgyzstan's decision to evict U.S. forces from its Manas air base, a decision that was made after Bishkek received a $2 billion loan from Russia.
Lukyanov adds that the first meeting between the two is important, as Obama and Medvedev will each be "sizing up his counterpart to see what he is made of."
Lukyanov says, however, that it would be a mistake to overestimate the personal aspect of the relationship, noting that despite close personal ties between Bush and former Russian President -- and current prime minister -- Vladimir Putin, relations nevertheless deteriorated.
Nevertheless, Masha Lipman of the Moscow Carnegie Center says the dynamic between the two presidents will be important in setting a new tone in the relationship.
"The main problem isn't even the issues and the disagreement between the two sides," Lipman says. "The most important thing, in my opinion, is the atmosphere of deep mistrust."
U.S.-Russian relations have deteriorated in recent years to the lowest point since the early 1980s. Moscow has complained about Washington's missile defense plans as well as its efforts to bring Georgia and Ukraine into NATO.
For its part, the United States has criticized Russia for backsliding on democracy and civil liberties at home and for bullying its neighbors in the former Soviet space.
Relations hit a low point following Russia's military incursion into Georgia in August 2008, which was launched after Tbilisi tried to take its pro-Moscow breakaway region of South Ossetia by force.
The Obama administration has announced its desire to "press the reset button" with Russia and improve relations. The Kremlin has made clear it expects Washington to initiate the effort by offering concessions.
White House press secretary Robert Gibbs says, however, that restoring relations will take efforts from both sides. Gibbs told reporters this week that "nobody believes that change in our relationship means giving everyone all they want... That's certainly not the intention of the president."
reported by RFE/RL correspondent Brian Whitmore and RFE/RL's Russian Service, with Reuters