Pakistanis with the most knowledge of the country’s nuclear program are among the most worried. On Dec. 16, 2014, the Taliban launched a deadly attack on an army-run school in the Pakistani city of Peshawar. Afterward, Pakistan’s Atomic Energy Commission sent an urgent letter to the director general of the Strategic Plans Division, which is responsible for securing Pakistan’s nuclear assets, expressing concern. The Atomic Energy Commission requested that the military devote more resources to ensuring that the personnel with knowledge of the nuclear program are monitored. This letter, which has been kept secret until now, reveals just how concerned some Pakistani officials are — and how worried the rest of the world should be.

The Atomic Energy Commission is not the only group sounding alarms about the role of extremists inside Pakistan. In early 2014, the ministry of interior issued a policy paper called the National Internal Security Policy 2014-2018, a classified document that outlined the government’s security priorities. It warns that Pakistan is home to hundreds of terrorist and extremist groups, and points out that many of them are operational in all four provinces of Pakistan, including in the areas in Punjab near some of Pakistan’s nuclear facilities. This document also raises concerns over the growing influence of certain terrorist groups, in particular Lashkar-e-Taiba, inside the Pakistan Army and intelligence agencies, and within the families of senior and midlevel military officers.

Despite all of this, the Pakistani authorities continue to insist in public that their nuclear assets are safe. As a senior official told The Atlantic magazine in 2011, “Of all the things in the world to worry about, the issue you should worry about the least is the safety of our nuclear program.” When Pakistani officials came to Washington for a nuclear security summit last spring, they affirmed in the broadest terms their country’s commitment to nuclear security from “the entire spectrum of threats” — playing down terrorism specifically, or the fact that Pakistan represents a particular threat.

The Pakistanis say they are confident in the Strategic Plans Division’s professionalism. And the division claims to have strong systems in place to screen personnel for integrity, weeding out those who have dangerous political, ethnic or religious affiliations. They also report that Pakistan’s nuclear weapons are de-mated, meaning the warheads are separated from their delivery mechanisms. But even if this is true, it doesn’t mean that all nuclear material is safe. There are reports that Pakistan is building tactical nuclear weapons, smaller arms that are easier to use on the battlefield. It is unclear how the Strategic Plans Division intends to secure them.

Instead of asking for help dealing with these vulnerabilities, the Pakistani Army and intelligence community close themselves off. They fear that the United States is trying to seize their nuclear weapons and say that the West refuses to allow a Muslim country to have access to the world’s most powerful weapons, a line often repeated by extremists.