WASHINGTON – Pakistani Prime Minister Yusuf Raza Gilani said Monday that his country’s nuclear weapons are well-guarded, rebutting misgivings by nuclear experts about the safety of the small but growing arsenal.

“Islamabad has taken effective steps for nuclear safety, security and nonproliferation through extensive legislative, regulatory and administrative framework,” said Gilani, who was in Washington for a historic 47-nation nuclear security summit.

A new report from a Harvard nonproliferation expert, released Monday, finds that Pakistan’s stockpile faces “immense” threats and is the world’s least secure from theft or attack.

President Obama, who hosted the summit, is trying to persuade world leaders to confront the threat that nuclear arms might fall into the hands of terrorists, a possibility he describes as the biggest threat to global security.

Pakistan’s leaders insist their stockpiles are safe and contend their country follows the regulations set by the International Atomic Energy Agency.

“We are confident our system is second to none,” said Foreign Minister Shah Mahmood Qureshi. “We have world-class measures in place.”

The study, commissioned by the Nuclear Threat Initiative and released by Harvard University’s Belfer Center for Science and International Affairs, found that Pakistan faces formidable risks in safeguarding its nuclear warheads.

While acknowledging substantial security improvements in the last few years, the study notes that the danger persists from “nuclear insiders with extremist sympathies, al-Qaida or Taliban outsider attacks, and a weak state.”