Russia and the United States open fresh nuclear disarmament negotiations this week under pressure to strike a deal by year's end that experts say will have far-reaching consequences for world security.
The talks mark the resumption, after a generation of drift, of a process begun in 1969 at the height of the Cold War and are a central element of US President Barack Obama's stated desire to "reset" frayed ties with Russia.
The initial two-day negotiating session was due to start Tuesday. Heads of the US and Russian delegations held a technical meeting in Rome last month, but the Moscow talks marked the formal start of the process, officials said.
Disagreements between the two countries on the size, nature and purpose of their nuclear arsenals and strategic weapons systems abound, but both have indicated recently that the political will to overcome them now exists.
"There are good chances for bringing our positions closer and for working out agreements," Russian Foreign Minister Sergei Lavrov said last week after meeting US Secretary of State Hillary Clinton in Washington.
Pressure on negotiators was heightened after the White House announced Obama will travel to Moscow on July 6 for a summit meeting with his Russian counterpart Dmitry Medvedev on reducing nuclear weapons arsenals and other security challenges.
The meeting will allow the United States and the Russian Federation an opportunity "to deepen engagement on reducing nuclear weapons, cooperating on non-proliferation, exploring ways to cooperate on missile defense, addressing mutual threats and security challenges," the White House said in a statement.
The main agreement governing US and Russian strategic nuclear weapons, the Strategic Arms Reduction Treaty (START), expires on December 5 and there has so far been little specific discussion on what the two sides should do next.
Areas of discord include the limits on nuclear warhead numbers, whether the treaty should cover delivery systems like bombers and missiles, verification procedures and other issues of information sharing and confidence-building.
But despite the technical complexity and tight schedule of the negotiations, both countries have deep-seated national interests in ensuring the talks happen and conclude with results both can hold up to the world as meaningful progress.
The format of the talks gives Russia strategic "parity" with the United States, a matter diplomats say is of huge importance to Moscow as it seeks to recover global prestige enjoyed prior to the 1991 collapse of the Soviet Union.
And a return to direct engagement in substance with Moscow on a bilateral matter of international importance helps dispel perceptions that Washington acts unilaterally and will smooth cooperation with Russia on other issues.
That the United States has a need to enter disarmament talks with Russia for reasons that go beyond just limiting nuclear weapons was acknowledged in a report published earlier this month by a high-level Washington policy group.
"The moment appears ripe for a renewal of arms control with Russia," the Congressional Commission on the Strategic Posture of the United States, headed by former defense secretary William Perry, said.
"In support of its arms control interests and interest in strategic stability more generally, the United States should pursue a much broader and more ambitious set of strategic dialogues" with Russia and others, it said.
For Vladimir Dvorkin, a retired general involved on the Soviet side in the landmark Strategic Arms Limitation Talks (SALT) of the 1970s and the START talks of the 1980s, the new US-Russia negotiations are of major significance.
"It is not just about the numbers of weapons," Dvorkin told AFP. "The process itself is important, because the idea of total nuclear disarmament is out there now.
"The process is long -- it will take decades. But it is necessary, because in the final analysis the liquidation of all nuclear weapons is a prerequisite for a new global security arrangement that is not based on the threat of force," he said.
The US delegation to the negotiations is headed by Assistant Secretary of State Rose Gottemoeller while the Russian delegation is headed by Anatoly Antonov, head of the foreign ministry department for security and disarmament.