Nuclear Weapons

Little more than a year after U.S. spy agencies concluded that Iran had halted work on a nuclear weapon, the Obama administration has made it clear that it believes there is no question that Tehran is seeking the bomb. In his news conference this week, President Obama went so far as to describe Iran's "development of a nuclear weapon" before correcting himself to refer to its "pursuit" of weapons capability. Obama's nominee to serve as CIA director, Leon E. Panetta, left little doubt about his view last week when he testified on Capitol Hill.

Secretary of State Hillary Rodham Clinton warned Wednesday that the United States may erect a "defense umbrella" over the Middle East if Tehran continues its nuclear program, a sign that the Obama administration is preparing for the reality of an Iranian bomb.

The United States and allied powers threatened Monday to impose new penalties on North Korea after the defiant regime announced its second nuclear bomb test, but their leverage in derailing the weapons program appeared limited. The five permanent members of the United Nations Security Council, meeting in emergency session in New York, denounced the test as a "clear violation" of a 2006 resolution.

A decadelong effort to refurbish thousands of aging nuclear warheads has run into serious technical problems that have forced delays and exacerbated concerns about the Energy Department's ability to maintain the nation's strategic deterrent. The program involves a type of warhead known as the W76, which is used on the Navy's Trident missile system and makes up more than half of the deployed warheads in the U.S. stockpile.

U.S. Defense Secretary Robert M. Gates promised today to hold North Korea accountable for selling or transferring nuclear material outside its borders, providing the first clear expression of the Obama administration's thinking on a vexing foreign policy challenge. A succession of U.S. presidents have tried to persuade the reclusive government to give up its nuclear arms, and Gates made it clear that President Obama was open to using diplomacy to end the threat.

Attempts to control or reverse nuclear proliferation come in two flavors: Either one tries to control nuclear material (uranium, centrifuges, superfast switches) or one tries to control nuclear information (blueprints, schematics, scientific expertise). For most of the last half a century, the world has shunned the material approach in favor of controlling information. But information is extremely difficult to contain, as is made clear by the growing number of countries that have acquired nuclear weapons in the decades since the United States made the first atomic bomb, from the Soviet Union in 1949 to North Korea in 2006.

Further sanctions against Iran would be "counterproductive," Russia's top diplomat said today, pushing back pointedly against U.S. pressure for a tougher stance against Tehran's nuclear ambitions. The remarks from Russian Foreign Minister Sergei Lavrov, delivered at the side of Secretary of State Hillary Rodham Clinton, appeared to undercut hopes that Moscow might agree to additional steps that would isolate Iran. "We believe that at this stage all efforts must be focused on supporting the negotiating process," Lavrov said.

Russia closed down another plutonium-producing reactor as part of a years-long effort by Moscow and Washington to shutter the Cold War-era facilities that produced material for nuclear weapons. Workers will begin removing the remaining uranium fuel from the ADE-5 reactor at the Siberian Chemical Plant in Seversk, said the atomic energy agency, Rosatom. The plant's first reactor was shut down April 20. Russia's last plutonium-producing reactor, in Zheleznogorsk, is expected to be shuttered by 2010.

Iranian Vice President Gholamreza Aghazadeh signaled that Tehran will no longer cooperate with U.N. experts looking for signs of clandestine nuclear weapons work. Iran insists that its only goal is to produce fuel for nuclear reactors to generate electricity. It dismisses as fabricated evidence supplied by the U.S. and other members of the International Atomic Energy Agency's governing board that purportedly backs allegations that it continues to work on nuclear weapons. Aghazadeh said investigating such allegations "is outside the domain of the agency."

President Obama vowed Sunday to pursue the elimination of nuclear weapons from the planet, telling a cheering throng in Prague that the United States is ready to lead an international effort to reduce atomic arsenals and the threat they pose. Speaking only hours after North Korea launched a multistage rocket, drawing new international concern and condemnation, Obama outlined a plan to work toward a goal that he acknowledged remains decades away.