The New York Times reports senior US officials are increasingly concerned about new vulnerabilities for Pakistan’s nuclear arsenal, including the potential for militants to snatch a weapon in transport. Concerns have intensified in the last two weeks since the Taliban entered Buner, a district sixty miles from the capital, Islamabad. The US is currently spending $100 million a year on a secret program to help Pakistan build stronger physical protections around their nuclear weapons facilities, but the Times reports the US does not even know the location of all of Pakistan’s nuclear sites. Meanwhile, The Guardian reports Pakistan is continuing to expand its nuclear bomb-making facilities. Commercial satellite photos show two plutonium-producing reactors are nearing completion at Khushab, about 160 miles southwest of Islamabad. Pakistani President Asif Ali Zardari is scheduled to visit President Obama in Washington on Wednesday.