The highest-ranking U.S. military officer said on Thursday that Pakistan's control over its nuclear weapons appears tight enough to protect against the possibility of seizure by extremist sympathizers who might infiltrate the nation's army or intelligence service.
Over time, Washington has seen the South Asian nation's atomic arsenal become "physically more secure," Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, said at the Defense Department. "We've seen the training improve" for personnel entrusted with handling and guarding the weapons, he said.
Pakistan "in recent years" has also introduced a "personnel reliability program" of sorts for its nuclear security forces that involves "a very difficult screening process," Mullen told reporters at a round-table discussion held a few steps from his Pentagon office.
A similar effort set up to help protect U.S. nuclear weapons demands that the vetting of military personnel is routinely updated as a condition of their continued access to these most sensitive arms. There are also a number of strict rules they "have to continue compliance with," said the chairman, who suggested that further public elaboration could heighten any security risks.
The JCS chairman and others have said the Energy Department has invested in helping Islamabad improve its ability to safeguard the Pakistani nuclear stockpile.
"We have offered any assistance that Pakistan might desire with respect to [the] means for security of nuclear weapons," James Miller, the principal deputy Defense undersecretary for policy, said at a May 4 Senate Armed Services Strategic Forces Subcommittee hearing.
Mullen's latest comments echo several prior expressions of confidence in Islamabad's ability to prevent violent extremists from stealing a nuclear weapon, or secreting away fissile material for constructing a "dirty bomb" capable of spreading radioactive particles.
Concern about this risk has recently been heightened, though, following the May 2 U.S. raid on Osama bin Laden's secret compound in Abbottabad, resulting in the al-Qaida leader's death.
After poring over documents and electronic media seized in the Navy SEAL operation, the U.S. intelligence community apparently has found no direct evidence that Pakistani officials were aware of or facilitating the terrorist icon's hideout, Mullen said on Thursday.
However, a number of top Obama administration officials -- including the president himself -- suspect that bin Laden relied on Pakistani assistance, perhaps at mid-levels of the army or intelligence service.
"There had to be some sort of support network for bin Laden inside of Pakistan," Obama said in an interview with CBS News' 60 Minutes aired on May 8. "But we don't know who or what that support network was."
Following the Abbottabad operation, Washington's relations with Islamabad have become increasingly strained. Among other troubling developments, Pakistan last month arrested five informants who had helped develop CIA information on bin Laden's whereabouts. The action reinforced doubts in some quarters about the two nations' partnership in countering terrorists.
"We're going through a very difficult time of reassessment right now," Mullen told reporters. "I'm not exactly sure how it comes out and what the specifics would be. But I hope that as we work our way through this, we're able to sustain this relationship."
A number of lawmakers on Capitol Hill are calling for reductions in the $2 billion in annual U.S. aid to Pakistan. The U.S. House on Thursday rejected two proposals for deep funding cuts, though additional votes on decreasing the amount of assistance might yet occur, The Hill reported.
A late-May Taliban attack against a Pakistani naval air base in Karachi has further stoked concerns about an extremist presence inside the nation's military apparatus. The violent Islamists were able to pass through a number of security positions and even appeared to know where surveillance cameras were located as they carried out a protracted offensive, leading many to conclude that the attackers had assistance from within.
One expert recently told National Public Radio that the Karachi attack and other similar incidents appear to offer a blueprint for some future militant strike on a location where Pakistani nuclear weapons are kept.
"I think we are looking at the possibility of a very serious breach of Pakistan's nuclear security before too long," Shaun Gregory, an expert on Pakistan at the University of Bradford in the United Kingdom, was quoted as saying.
An extremist attack on a Pakistani nuclear base would almost certainly necessitate inside assistance, according to nuclear security specialist David Albright. Gaining access to a warhead would require not only passing through base security but also getting inside an underground bunker, he told Global Security Newswire in a May 16 telephone interview.
A more likely scenario might be that militants or their sympathizers are able to divert nuclear material during the weapon-production process, where many more people come into contact with sensitive items, said Albright, president of the Institute for Science and International Security. Individuals might divert small amounts of bomb-making material -- or perhaps already have done so -- without anyone else knowing, he said.
Pakistan has the world's fastest growing nuclear arsenal and could have as many as 200 warheads within the next 10 years, according to an analysis published this week in the Bulletin of the Atomic Scientists. Islamabad today is estimated to have 90 to 110 atomic arms.
Despite the "positive steps" that Pakistan has taken to safeguard its stockpile, there are constraints on how much information the United States has been able to obtain about the South Asian country's nuclear weapons or infrastructure, Mullen acknowledged.
Pakistani leaders have maintained tight secrecy over exactly how many nuclear arms they have and where they are located, out of concerns that neighboring rival India or the United States might someday take steps to seize them, regional experts say.
"There are limits to what I know and to what anybody outside Pakistan knows," Mullen said. "But I know that they have invested a great deal, they've improved their procedures, and they take it very seriously."
Ultimately, though, "this is a sovereign country," he said. "These are their weapons. There are limits to what we know in that regard."