Israel has kept nuclear weapons behind a garment-factory cover for more than 60 years

Israel said it was building a 'textile factory' in the Negev desert. Behind that cover, however, a nuclear facility was taking shape. Even after learning the truth, the United States stayed publicly silent about Israel's nuclear weapons programme for more than six decades.

In the early 1960s, several American diplomats were travelling in an Israeli helicopter when one of them spotted construction under way in the Negev desert, about 20 miles west of the Dead Sea. Asked what the facility was, Israeli finance ministry official Addy Cohen told US Ambassador Ogden Reid that a textile factory was being built there. It later emerged that the site was the Dimona nuclear centre.

A few years later, US nuclear officials detected that hundreds of pounds of weapons-grade enriched uranium had gone missing from a uranium plant in Pennsylvania. Some American intelligence officers believed the uranium had been diverted for use in Israel's nuclear programme. The claim has also surfaced in a recent documentary.

Since then, both the United States and Israel have maintained a public stance of ambiguity on nuclear weapons. Israel has never formally admitted owning nuclear weapons, and the United States has never taken a direct position on the matter either.

In the words of Israeli-American historian Avner Cohen, the matter has over time become the world's 'worst-kept secret'. But the silence is not only a diplomatic tactic; behind it lie the goals of preventing the spread of nuclear weapons in the Middle East and the political calculations of the US-Israel relationship.

Matthew Kroenig, a professor of political science at Georgetown University and a nuclear strategist, told CNN that if Israel publicly declared itself a nuclear-armed state, other countries in the Middle East would come under pressure to follow the same path. That could trigger an uncontrolled nuclear arms race in the region, which would not serve US interests.

According to experts, this policy of secrecy has been in force since the Cold War. The United States and Israel feared that openly acknowledging Israel's nuclear capability could prompt Arab states, backed by the Soviet Union, to pursue nuclear weapons of their own. At the same time, Israel feared that coming out publicly as a nuclear-armed state would expose it to diplomatic pressure internationally.

In the same year the missing enriched uranium from the Pennsylvania plant was detected, then US Secretary of State Henry Kissinger visited Israel. After discussions with Israeli officials during the visit, he informed senior officials at the US embassy about the matter.

A summary of those discussions, preserved in the US National Security Archive, says Kissinger firmly believed Israel had already begun a nuclear weapons programme. Earlier, President John F. Kennedy had also tried to stop such a programme in Israel.

In July 1969, Kissinger sent a memorandum to then President Richard Nixon. An accompanying report warned senior US officials that Israel's acquisition of nuclear weapons would greatly increase the risk that someone might use a nuclear weapon in anger. In light of the situation, Nixon also threatened to halt arms supplies to Israel.

But Kissinger understood that merely threatening to cut off arms supplies might not be enough to stop Israel's nuclear programme. Such a step could anger the US Congress and create a crisis in domestic politics. On the other hand, bringing Israel's nuclear programme into the open and applying diplomatic pressure could lead the Soviet Union and Arab states to accuse the United States of aiding Israel. To avoid both risks, Washington adopted a policy of maintaining ambiguity on the matter. At the same time, Israel refused to sign the Nuclear Non-Proliferation Treaty (NPT).

In his memorandum, Kissinger wrote, "What we really want is for Israel's ownership of nuclear weapons not to become, at least, an internationally established fact."

In 1986, however, Israel's nuclear programme stirred fresh debate internationally. That year Mordechai Vanunu, a former reactor technician at the Dimona nuclear centre, disclosed details of Israel's secret nuclear programme. He also handed several photographs from inside the facility to the British newspaper The Sunday Times.

That brought much of the long-kept secrecy around Israel's nuclear capability into the open. Yet the country still has not formally admitted owning nuclear weapons, and the United States has not moved away from its long-standing policy of ambiguity on the issue.