Russia and the US agreed today to cut their nuclear warhead arsenals to as few as 1,500 each, aiming toward the lowest levels of any US-Russia arms control deal.
The initial agreement signed by presidents Barack Obama and Dmitry Medvedev at a Moscow summit, is meant to guide negotiators as the nations work toward a replacement pact for the START strategic arms control reduction treaty, which expires in December.
The joint understanding, signed after about three hours of talks at the Kremlin, also commits the new treaty to lower each nation's longer-range missiles for delivering nuclear bombs to between 500 and 1,100.
Under current treaties, each country is allowed a maximum of 2,200 warheads and 1,600 launch vehicles.
A White House statement said the new treaty "will include effective verification measures."
"The new agreement will enhance the security of both the US and Russia, as well as provide predictability and stability in strategic offensive forces," the statement said.
The leaders also announced several other deals meant to show progress toward repairing badly damaged US-Russian relations including Moscow allowing the United States to transport arms across its land and airspace into Afghanistan for the war there.
They outlined other ways to work together to help stabilise Afghanistan, including increasing assistance to the Afghan army and police and training counter-narcotics personnel. A joint statement said the United States and Russia welcomed increased international support for upcoming Afghan elections and they were prepared to help Afghanistan and Pakistan work together against the "common threats of terrorism, extremism and drug trafficking."
Other side agreements include reviving a joint commission to try to account for missing service members of both countries dating back to the Second World War and new cooperation on public health issues.
The commission was first created by the first President Bush and President Boris Yeltsin in the early 1990s, but the Russians later downgraded their participation. The US hope Russia will open some of its more sensitive archives to US researchers seeking details about missing American servicemen.
Mr Obama needs Russia's help chiefly in pressuring Iran and North Korea to give up their nuclear weapons ambitions, but also in tackling terrorism, global warming and the economy. But with relations frayed with Moscow's war with Georgia last year and US missile defence plans in eastern Europe, Mr Obama's desire to reset relations is a huge test of his diplomatic skills.
"The United States and Russia have more in common than they have differences," Mr Obama said as he and Medvedev first sat down.
His host launched the high-stakes summit with similar good will.
"We'll have a full-fledged discussion of our relations between our two countries, closing some of the pages of the past and opening some of the pages of the future," Mr Medvedev said.
However the two sides remain at stalemate over the US pursuit of a missile-defence system in Europe, pushed hard by Mr Bush and under review by Mr Obama.
The US insists it is designed to protect US allies in Europe from a potential nuclear attack by Iran. But the Russians see it as a first step toward a system that could weaken their offensive nuclear strike potential.
The summit starts a week-long trip for Mr Obama that also features G8 meetings and a visit with the pope in Italy, and a speech in Ghana.