Switzerland and the militant Palestine Liberation Organization (PLO) concluded a secret deal in 1970 to avert further terrorist attacks against the country.
The Neue Zürcher Zeitung (NZZ) newspaper says a delegation led by Foreign Minister Pierre Graber met senior PLO officials in Geneva to negotiate a pact offering diplomatic support for the Palestinian cause in return for assurances to be spared from attacks.
The first contacts between the Swiss minister and the Palestinians were initiated by Jean Ziegler, according to the NZZ. The controversial leftwing human rights advocate was a member of the Swiss parliament at the time.
The confidential negotiations risked creating a diplomatic crisis with the United States, Britain, Germany and Israel, according to the report.
Details of the agreement are still locked away under a 50-year statute of limitations.
Speaking on public radio SRF, Ziegler confirmed his role as go-between and advisor for the foreign minister. However, he declined to say whether he took part in secret meetings.
The 81-year old former professor of sociology said the secret deal was "immoral" and in breach of legal principles, but it was justified for strategic reasons.
"This might be absolutely shocking, but the reward was that there were no more attacks," he said.
However, the foreign policy research centre Diplomatic Documents of Switzerland downplays the importance of the reported contacts between Switzerland and PLO officials.
"The talks by Graber in Geneva in September 1970 were not known before, but they are unlikely to have had a decisive impact on further developments in relations between Switzerland and the PLO," a statement said on Wednesday.
The experts say they found no trace of the Geneva meeting in official documents.
They doubt whether closer official ties with PLO representatives in the mid 1970s were directly connected to the alleged secret deal.
However, the government was clearly interested to let the PLO set up an office in Geneva to "reduce the danger of terror attacks in Switzerland", as the research centre quotes official documents.
Attacks and hijacking
In February 1970 a Swissair passenger plane bound for Tel Aviv crashed shortly after take-off in Zurich, killing all 47 people on board. But the suspected mastermind of the bomb attack, a Jordanian national, was never taken to court.
A year before, a pilot of the Israeli El Al airline was killed by four Palestinian attackers at Zurich airport.
In September 1970, a Swissair flight bound for New York was hijacked by a Palestinian commando and flown to Jordan to force the handing over of jailed Palestinian militants in Switzerland. Passengers of a US and British jet were also held hostage in Jordan.
The report comes as the NZZ publishing house launches a book by one of its journalists, Marcel Gyr, who spoke primarily to former Palestinian and Swiss officials as well as Ziegler.
Urs Geiser, swissinfo.ch