Among the hours of covert tape recordings, she says she heard evidence that one well-known senior official in the US State Department was being paid by Turkish agents in Washington who were selling the information on to black market buyers, including Pakistan.

The name of the official – who has held a series of top government posts – is known to The Sunday Times. He strongly denies the claims.

However, Edmonds said: “He was aiding foreign operatives against US interests by passing them highly classified information, not only from the State Department but also from the Pentagon, in exchange for money, position and political objectives.”

She claims that the FBI was also gathering evidence against senior Pentagon officials – including household names – who were aiding foreign agents.

“If you made public all the information that the FBI have on this case, you will see very high-level people going through criminal trials,” she said.

Her story shows just how much the West was infiltrated by foreign states seeking nuclear secrets. It illustrates how western government officials turned a blind eye to, or were even helping, countries such as Pakistan acquire bomb technology.

The wider nuclear network has been monitored for many years by a joint Anglo-American intelligence effort. But rather than shut it down, investigations by law enforcement bodies such as the FBI and Britain’s Revenue & Customs have been aborted to preserve diplomatic relations.

Edmonds, a fluent speaker of Turkish and Farsi, was recruited by the FBI in the aftermath of the September 11 attacks. Her previous claims about incompetence inside the FBI have been well documented in America.

She has given evidence to closed sessions of Congress and the 9/11 commission, but many of the key points of her testimony have remained secret. She has now decided to divulge some of that information after becoming disillusioned with the US authorities’ failure to act.

One of Edmonds’s main roles in the FBI was to translate thousands of hours of conversations by Turkish diplomatic and political targets that had been covertly recorded by the agency.

A backlog of tapes had built up, dating back to 1997, which were needed for an FBI investigation into links between the Turks and Pakistani, Israeli and US targets. Before she left the FBI in 2002 she heard evidence that pointed to money laundering, drug imports and attempts to acquire nuclear and conventional weapons technology.

“What I found was damning,” she said. “While the FBI was investigating, several arms of the government were shielding what was going on.”

The Turks and Israelis had planted “moles” in military and academic institutions which handled nuclear technology. Edmonds says there were several transactions of nuclear material every month, with the Pakistanis being among the eventual buyers. “The network appeared to be obtaining information from every nuclear agency in the United States,” she said.

They were helped, she says, by the high-ranking State Department official who provided some of their moles – mainly PhD students – with security clearance to work in sensitive nuclear research facilities. These included the Los Alamos nuclear laboratory in New Mexico, which is responsible for the security of the US nuclear deterrent.

In one conversation Edmonds heard the official arranging to pick up a $15,000 cash bribe. The package was to be dropped off at an agreed location by someone in the Turkish diplomatic community who was working for the network.

The Turks, she says, often acted as a conduit for the Inter-Services Intelligence (ISI), Pakistan’s spy agency, because they were less likely to attract suspicion. Venues such as the American Turkish Council in Washington were used to drop off the cash, which was picked up by the official.

Edmonds said: “I heard at least three transactions like this over a period of 2½ years. There are almost certainly more.”

The Pakistani operation was led by General Mahmoud Ahmad, then the ISI chief.

Intercepted communications showed Ahmad and his colleagues stationed in Washington were in constant contact with attachés in the Turkish embassy.

Intelligence analysts say that members of the ISI were close to Al-Qaeda before and after 9/11. Indeed, Ahmad was accused of sanctioning a $100,000 wire payment to Mohammed Atta, one of the 9/11 hijackers, immediately before the attacks.

The results of the espionage were almost certainly passed to Abdul Qadeer Khan, the Pakistani nuclear scientist.

Khan was close to Ahmad and the ISI. While running Pakistan’s nuclear programme, he became a millionaire by selling atomic secrets to Libya, Iran and North Korea. He also used a network of companies in America and Britain to obtain components for a nuclear programme.

Khan caused an alert among western intelligence agencies when his aides met Osama Bin Laden. “We were aware of contact between A Q Khan’s people and Al-Qaeda,” a former CIA officer said last week. “There was absolute panic when we initially discovered this, but it kind of panned out in the end.”

It is likely that the nuclear secrets stolen from the United States would have been sold to a number of rogue states by Khan.

Edmonds was later to see the scope of the Pakistani connections when it was revealed that one of her fellow translators at the FBI was the daughter of a Pakistani embassy official who worked for Ahmad. The translator was given top secret clearance despite protests from FBI investigators.

Edmonds says packages containing nuclear secrets were delivered by Turkish operatives, using their cover as members of the diplomatic and military community, to contacts at the Pakistani embassy in Washington.

Following 9/11, a number of the foreign operatives were taken in for questioning by the FBI on suspicion that they knew about or somehow aided the attacks.

Edmonds said the State Department official once again proved useful. “A primary target would call the official and point to names on the list and say, ‘We need to get them out of the US because we can’t afford for them to spill the beans’,” she said. “The official said that he would ‘take care of it’.”

The four suspects on the list were released from interrogation and extradited.

Edmonds also claims that a number of senior officials in the Pentagon had helped Israeli and Turkish agents.

“The people provided lists of potential moles from Pentagon-related institutions who had access to databases concerning this information,” she said.

“The handlers, who were part of the diplomatic community, would then try to recruit those people to become moles for the network. The lists contained all their ‘hooking points’, which could be financial or sexual pressure points, their exact job in the Pentagon and what stuff they had access to.”

One of the Pentagon figures under investigation was Lawrence Franklin, a former Pentagon analyst, who was jailed in 2006 for passing US defence information to lobbyists and sharing classified information with an Israeli diplomat.

“He was one of the top people providing information and packages during 2000 and 2001,” she said.

Once acquired, the nuclear secrets could have gone anywhere. The FBI monitored Turkish diplomats who were selling copies of the information to the highest bidder.

Edmonds said: “Certain greedy Turkish operators would make copies of the material and look around for buyers. They had agents who would find potential buyers.”

In summer 2000, Edmonds says the FBI monitored one of the agents as he met two Saudi Arabian businessmen in Detroit to sell nuclear information that had been stolen from an air force base in Alabama. She overheard the agent saying: “We have a package and we’re going to sell it for $250,000.”

Edmonds’s employment with the FBI lasted for just six months. In March 2002 she was dismissed after accusing a colleague of covering up illicit activity involving Turkish nationals.

She has always claimed that she was victimised for being outspoken and was vindicated by an Office of the Inspector General review of her case three years later. It found that one of the contributory reasons for her sacking was that she had made valid complaints.

The US attorney-general has imposed a state secrets privilege order on her, which prevents her revealing more details of the FBI’s methods and current investigations.

Her allegations were heard in a closed session of Congress, but no action has been taken and she continues to campaign for a public hearing.

She was able to discuss the case with The Sunday Times because, by the end of January 2002, the justice department had shut down the programme.

The senior official in the State Department no longer works there. Last week he denied all of Edmonds’s allegations: “If you are calling me to say somebody said that I took money, that’s outrageous . . . I do not have anything to say about such stupid ridiculous things as this.”

In researching this article, The Sunday Times has talked to two FBI officers (one serving, one former) and two former CIA sources who worked on nuclear proliferation. While none was aware of specific allegations against officials she names, they did provide overlapping corroboration of Edmonds’s story.

One of the CIA sources confirmed that the Turks had acquired nuclear secrets from the United States and shared the information with Pakistan and Israel. “We have no indication that Turkey has its own nuclear ambitions. But the Turks are traders. To my knowledge they became big players in the late 1990s,” the source said.

How Pakistan got the bomb, then sold it to the highest bidders

1965 Zulfikar Ali Bhutto, Pakistan’s foreign minister, says: “If India builds the bomb we will eat grass . . . but we will get one of our own”

1974 Nuclear programme becomes increased priority as India tests a nuclear device

1976 Abdul Qadeer Khan, a scientist, steals secrets from Dutch uranium plant. Made head of his nation’s nuclear programme by Bhutto, now prime minister

1976 onwards Clandestine network established to obtain materials and technology for uranium enrichment from the West

1985 Pakistan produces weapons-grade uranium for the first time

1989-91 Khan’s network sells Iran nuclear weapons information and technology

1991-97 Khan sells weapons technology to North Korea and Libya

1998 India tests nuclear bomb and Pakistan follows with a series of nuclear tests. Khan says: “I never had any doubts I was building a bomb. We had to do it”

2001 CIA chief George Tenet gathers officials for crisis summit on the proliferation of nuclear technology from Pakistan to other countries

2001 Weeks before 9/11, Khan’s aides meet Osama Bin Laden to discuss an Al-Qaeda nuclear device

2001 After 9/11 proliferation crisis becomes secondary as Pakistan is seen as important ally in war on terror

2003 Libya abandons nuclear weapons programme and admits acquiring components through Pakistani nuclear scientists

2004 Khan placed under house arrest and confesses to supplying Iran, Libya and North Korea with weapons technology. He is pardoned by President Pervez Musharraf

2006 North Korea tests a nuclear bomb

2007 Renewed fears that bomb may fall into hands of Islamic extremists as killing of Benazir Bhutto throws country into turmoil