An apartheid-era cabinet minister carried a "nuclear trigger" to South Africa from Israel as part of Pretoria's efforts to build an atom bomb, according to a report in a Johannesburg newspaper.

Two renowned South African journalists have revealed that Eschel Rhoodie, the apartheid government's information minister who played a central role in establishing military ties to Israel, privately described in 1979 how he had transported "the trigger" as hand luggage on a flight from Tel Aviv. But they say they were unable to publish the account at the time because of censorship and the former minister's concerns for his safety.

Allister Sparks – who in the 70s was editor of the influential but now defunct Rand Daily Mail – said he decided to go public with Rhoodie's admission, despite previous guarantees of secrecy, following last week's revelations in the Guardian and in a new book, The Unspoken Alliance, that Israel offered to sell nuclear warheads to apartheid South Africa.

Writing in the Business Day newspaper, Sparks said Rhoodie travelled regularly to Israel in the mid-70s, and on occasions was accompanied by South Africa's then intelligence chief, Hendrik van den Bergh.

"Rhoodie said talks had taken place between the two sides which had ultimately led to he and Van den Bergh being assigned the task of bringing "the trigger" to SA – which he said they did by packing it in a tea chest and transporting it as part of their hand-luggage on a South African Airways commercial flight," Sparks wrote.

Rhoodie later revealed the information to the Rand Daily Mail's chief investigative reporter, Mervyn Rees, whose work had exposed a government-run slush fund that brought down the then president, John Vorster, and the minister himself.

Rees confirmed Sparks's account to the Guardian, adding that Rhoodie did not give full details about the "trigger".

"I questioned him about it and he said I can't give you any of the details but suffice to say it was a vital component, it was a trigger, that would be used for South Africa's nuclear capability," said Rees.

It is possible that what Rhoodie called a trigger was tritium, a radioactive isotope required to explode certain types of nuclear bombs. It has been revealed, although not officially acknowledged, that Israel supplied South Africa with 30g of tritium in the mid-70s, enough to build a dozen atom bombs.

Apartheid-era officials have denied the tritium was used as part of the country's nuclear weapons programme and have pointed out that ultimately South Africa developed a type of atomic bomb that did not require that particular radioactive isotope.

But Sparks and Rees note that Rhoodie clearly said that what he called the trigger was delivered from Israel as part of South Africa's development of a nuclear weapon which provides further evidence that the two countries were co-operating.

Rhoodie, who died in 1993, told Rees that he became a point man in dealing with the Israelis after developing contacts while taking diving holidays in an Israeli resort. Rhoodie's meetings with the then Israeli defence minister, Shimon Peres, were an important step in establishing what would become very close collaboration in developing weapons. Peres, who is now Israel's president, wrote a letter to Rhoodie in 1974 praising the South African's leading role in initiating "a vitally important co-operation between the two countries".

Rees said Rhoodie confided in him during a series of lengthy conversations in Ecuador and then the south of France after he had been driven from office after the scandal over tens of millions of funds diverted from the defence budget to secret propaganda projects.

Rees said that although his reporting in the Rand Daily Mail was instrumental in exposing the scandal, Rhoodie was angered by what he viewed as his scapegoating by others in the government and decided to reveal what he knew about secret projects.

Rees said that during a meeting with Rhoodie in France in March 1979, Van den Bergh called the former minister to a meeting in Paris.

"He went off and came back the next day in a state of some agitation and said he'd been virtually threatened by Van den Bergh, not on behalf of the South Africans but by the Israelis in terms of any disclosure that might be made regarding South Africa's nuclear capability. He was clearly shaken about it," said Rees.

Rhoodie touched on Van den Bergh's warning in his 1983 book, The Real Information Scandal.

"I had obtained much of this top secret information for the simple reason that I was one of the people who pioneered relations with certain states overseas," he wrote. "I assured [Van den Bergh] that the various projects which he was concerned about would never be released unless, I said, I were to die an unnatural death."

Rhoodie and Rees became friends during the interviews, with Rees at one point delivering food and helping to care for the former minister when he was locked up in a French prison after the South African government sought his extradition over allegations of embezzling state funds.

Rees said he believes Rhoodie's account because he proved to have given reliable accounts of other secret operations.

Rhoodie agreed to talk to the Rand Daily Mail on the condition he could withhold publication of information he ultimately decided should not be disclosed. He applied that to the revelations about the nuclear cooperation.

Sparks said that the censorship laws of the time would have prevented him from printing it. But today he said that with Rhoodie no longer alive and fresh revelations about South Africa's nuclear ties to Israel, the time had come to reveal the truth.

"We do so because we believe it is now clear that there was nuclear collaboration between Israel and South Africa that enabled both sides to develop the bomb – and that given the state of nuclear proliferation in the world today it is in the global public interest that all available information about shady dealings with these apocalyptic weapons be brought into the open," Sparks wrote.

In response to the latest revelations, Peres's spokesperson, Ayalet Frisch, pointed to a statement by the former South African president, FW de Klerk, that his country had not co-operated with any foreign government in developing its nuclear weapons.

De Klerk made a similar claim to the South African parliament in 1993 when he said that the country at no point acquired nuclear weapons technology or materials from another state nor did it co-operate with foreign governments in developing its atomic bombs. However, that has since been challenged by revelations about the amount of yellowcake uranium South Africa supplied to Israel, the tritium deliveries and the joint development and testing in South Africa of missiles to carry nuclear weapons.