By Julian Borger
http://www.guardian.co.uk/world/2010/apr/12/pakistan-nuclear-weapons-security-fears

Pakistan yesterday came under increased pressure over its nuclear arsenal when a Harvard study warned of "a very real possibility" that its warheads could be stolen by terrorists.

The rising concern about poorly-guarded nuclear weapons and material was the subject of an extraordinary two-day summit which began in Washington yesterday. Last night, Ukraine became the latest country to volunteer to give up its stores of highly enriched uranium (HEU), which can be used in weapons, and switch its research reactors to low-enriched uranium.

There was still considerable anxiety at the Nuclear Security Summit over the safety of more than 2,000 tons more HEU and weapons-grade plutonium stored in 40 countries. There were also persistent doubts over the security of Pakistan's nuclear weapons.

Pakistan's prime minister, Yousaf Raza Gilani, assured Barack Obama the country has an "appropriate safeguard" for its arsenal, understood to consist of 70-90 nuclear weapons.

However, a report by Harvard University's Belfer Centre for Science and International Affairs, titled Securing the Bomb 2010, said Pakistan's stockpile "faces a greater threat from Islamic extremists seeking nuclear weapons than any other nuclear stockpile on earth".

Experts said the danger was growing because of the arms race between Pakistan and India. The Institute for Science and International Security has reported that Pakistan's second nuclear reactor, built to produce plutonium for weapons, shows signs of starting operations, and a third is under construction.

At their White House meeting on Sunday, Obama pressed Gilani to end Pakistan's opposition to an international treaty that would ban the production of new fissile material for nuclear warheads, plutonium and highly enriched uranium (HEU), but the Pakistani leader showed no signs of bowing to the pressure, US officials said.

Pakistan's insistence that India reduces its stockpile first prevented talks on the fissile material cutoff treaty from getting under way in Geneva last year. Yesterday, the UN secretary general, Ban Ki-moon, added to the pressure on Pakistan by calling for talks at the multilateral conference on disarmament to start, warning that "nuclear terrorism is one of the greatest threats we face today".

Both the US and Britain have declared themselves satisfied with Pakistan's security measures for its nuclear weapons, despite the rise of the Pakistani Taliban and other extremist groups. But yesterday's Harvard report said there were serious grounds for concern.

"Despite extensive security measures, there is a very real possibility that sympathetic insiders might carry out or assist in a nuclear theft, or that a sophisticated outsider attack (possibly with insider help) could overwhelm the defences," the report said.

It also warned that weaknesses remained in measures Russia had taken in recent years to guard its nuclear stockpile, the world's largest.

The nuclear security summit, which began yesterday in Washington, brings together leaders and officials from 47 nations, with the aim of focusing global attention on the danger of nuclear terrorism. The summit will endorse Obama's goal of locking up the world's stockpiles of plutonium or HEU within four years.

The Harvard report warned that the world "is not yet on track" to meet that deadline. Its author, Matthew Bunn said: "Sustained White House leadership will be needed to overcome complacency and convince policymakers around the world to act."

As a contribution to the aims of the summit, the US and Russia are due to sign an agreement in Washington to take 34 tonnes of weapons-grade plutonium out of their reserve stockpiles and use it for the generation of nuclear power. Other leaders are being called on to make concrete pledges in the main session today.

Last week, Malaysia adopted much-delayed export controls to prevent its ports being used as channels for the black market in nuclear equipment. Last month, Chile shipped all the HEU from its research reactors to the US for safekeeping.