The South African authorities have allowed Swiss investigators to examine documents in a probe of suspected criminal deals.
The Federal Prosecutor's Office said the Swiss team had been granted access to documents related to criminal proceedings in South Africa against Wouter Basson, the former director of South Africa's covert chemical weapons programme.
Two Swiss experts from the Prosecutor's Office and the Federal Police have just returned from a week in South Africa, where they investigated suspected illegal goods deliveries.
They were able to question several witnesses, including former high-ranking officials in South Africa. But the experts did not question Basson, according to an official statement published in Bern on Tuesday.
The Swiss prosecutor's office said it would carefully examine the documents as part of its investigation, which was launched three years ago.
It is the second time in two years that South Africa handed over documents to the Swiss authorities and granted legal assistance in investigations.
However, a spokesman for the federal prosecutor's office said the latest fact-finding mission to South Africa did not focus on allegations of links between Switzerland's intelligence services and the former Apartheid regime.
Two other probes
There are two other probes underway in Switzerland into alleged links between South Africa's apartheid regime and a former head of the Swiss military intelligence service, Peter Regli.
Last November a parliamentary committee decided to reopen investigations, after a previous investigation in 1999 had cleared Regli of any wrongdoing.
In addition, the Defence Ministry is carrying out its own probe into alleged close contact between Regli and Basson. It is also investigating accusations that Regli illegally destroyed documents.
At a court hearing in Pretoria last year, Basson alleged that Regli had helped in acquire 500 kilogrammes of the illegal drug, Mandrax, from Russia.
swissinfo with agencies