Image caption Pakistan says there have been no incidents involving its fissile material

US and UK diplomats feared Pakistan's nuclear material could fall into the hands of terrorists, the latest leaked classified US diplomatic cables reveal.

The documents, released by Wikileaks, warn that Pakistan is rapidly building its nuclear stockpile despite the country's growing instability.

There is also scepticism about whether Pakistan could cut links to militants.

A Pakistan spokesman quoted by AFP said the fears were "misplaced and fall in the realm of condescension".

Separately, Interpol has issued a notice asking for information on the whereabouts of Wikileaks founder, Julian Assange.

'Historical biases'

In one of the latest cables to be released by Wikileaks, senior UK Foreign Office official Mariot Leslie told US diplomats in September 2009 that Britain had "deep concerns about the safety and security of Pakistan's nuclear weapons".

In another cable seven months earlier, then-US ambassador Anne Patterson told Washington: "Our major concern is not having an Islamic militant steal an entire weapon but rather the chance someone working in government of Pakistan facilities could gradually smuggle enough material out to eventually make a weapon."

Analysis International concerns over the security of Pakistan's nuclear materials are not new, nor is Pakistan the only country to attract such concerns. But the stark language used in these confidential diplomatic cables gives us the clearest picture yet of what Western governments really fear - al-Qaeda or fellow jihadist militants getting their hands on enough nuclear material from Pakistan to build a crude nuclear device. This is thought unlikely to be a full-scale nuclear bomb but more feasibly a Radiological Dispersal Device (RDD), consisting of radioactive material wrapped around conventional explosive. If detonated it could scatter dangerous material over a wide area. The Pakistani media has expressed indignation in the past over any suggestion that the country's nukes are not secure. Some commentators have suggested this is deliberate scaremongering by the West so as to eventually seize control of Pakistan's strategic weapons.

Another cable concerning a US intelligence briefing in 2008 said: "Despite pending economic catastrophe, Pakistan is producing nuclear weapons at a faster rate than any other country in the world."

On Wednesday, Agence France-Presse news agency quoted Pakistan foreign office spokesman Abdul Basit as saying: "Their fears are misplaced and doubtless fall in the realm of condescension.

"There has not been a single incident involving our fissile material, which clearly reflects how strong our controls and mechanisms are. It is time they part with their historical biases against Pakistan."

Ms Patterson had also said there was "no chance" of Pakistan "abandoning support for [militant] groups".

The Pakistan government, she added, saw militant groups "as an important part of its national security apparatus against India".

The US also expressed concern about tensions between the powerful Pakistani army and President Asif Ali Zardari.

In material from March 2009, US cables noted that army chief General Ashfaq Parvez Kayani might "however reluctantly" put pressure on President Zadari to stop down, although he "distrusted [opposition leader] Nawaz [Sharif] even more".

Reliability questioned

The US has condemned the Wikileaks disclosures as an attack on the world community.

US Secretary of State Hillary Clinton said the diplomatic service relied, as did other professions such as law and medicine, on confidential communications to conduct some important business.

She said the international partnerships the US had worked hard to build would withstand the challenge posed by the leak cables.

The latest cache of messages, published by the UK Guardian newspaper, shows that Russia shared US and UK concerns over Pakistan.

Yuri Korolev, of the Russian foreign ministry, told US officials in February that "Islamists are not only seeking power in Pakistan but are also trying to get their hands on nuclear materials".

"There are 120,000-130,000 people directly involved in Pakistan's nuclear and missile programmes. There is no way to guarantee that all are 100% loyal and reliable," he said.

He said that extremists were able to recruit more easily.

"Pakistan has had to hire people to protect nuclear facilities that have especially strict religious beliefs, and recently the general educational and cultural levels in Pakistan has been falling," he says in the cable.

'Spoiled child'

The communications between the US State Department and its embassies and consulates around the world were sent between 1966 and 2010.

Other revelations from the despatches include:

China has become frustrated with North Korea behaving like a "spoiled child" and was coming around to the view that the Korean peninsula could become reunified under Seoul's leadership

Several Arab states, including Saudi Arabia, urged the US to take military action to bring an end to Iran's suspected nuclear weapons programme

Afghan President Hamid Karzai freed dangerous detainees and pardoned suspected drug dealers because they were linked to powerful or historically significant figures

Former UK Prime Minister Gordon Brown proposed a deal with the US in which suspected computer hacker Gary McKinnon plead guilty in return for a guarantee that he serve his sentence in the UK

Former British Guantanamo Bay detainee Moazzam Begg was praised by US ambassador to Luxembourg Cynthia Stroum for his campaign to persuade European countries to take in remaining inmates. Mr Begg was arrested by the CIA in 2002 and released from Guantanamo in 2005. He was never charged with any offence.

Wikileaks has so far posted only 291 of the 251,287 messages it says it has obtained. However, all of the messages have been made available to five publications, including the New York Times and the Guardian.

No-one has been charged with passing them to Wikileaks, but suspicion has fallen on US Army Private Bradley Manning, an intelligence analyst arrested in Iraq in June and charged over an earlier leak of a classified video.

On Tuesday, Wikileaks said it was coming under cyber-attack for the second time in three days. The Distributed Denial of Service (DDoS) attack, as it is known, works by flooding a target with too much data for it to handle.

The cables release is the third mass Wikileaks publication of classified documents; it published 77,000 secret US files on the Afghan conflict in July, and 400,000 documents about the Iraq war in October.

Meanwhile, Interpol has issued a "Red Notice" asking people to contact the police if they have any information about Mr Assange's whereabouts.

It said the Australian was wanted for questioning in Sweden over an alleged sex offence, which he has denied.