London (AFP) - A tip from a CIA spy to authorities in apartheid-era South Africa led to Nelson Mandela's arrest, beginning the leader's 27 years behind bars, a report said on Sunday.

Donald Rickard, a former US vice-consul in Durban and CIA operative, told British film director John Irvin that he had been involved in Mandela's arrest in 1962 which was seen as necessary because the Americans believed he was "completely under the control of the Soviet Union", the report in The Sunday Times newspaper said.

"He could have incited a war in South Africa, the United States would have to get involved, grudgingly, and things could have gone to hell," Rickard said.

"We were teetering on the brink here and it had to be stopped, which meant Mandela had to be stopped. And I put a stop to it."

Irvin's new film "Mandela's Gun", about the months before the anti-apartheid leader's arrest, is due to be screened at the Cannes film festival this week.

Mandela was eventually freed from prison in 1990 and went on to become South Africa's president between 1994 and 1999 before dying in 2013 aged 95.

Zizi Kodwa, national spokesman of Mandela's ruling African National Congress (ANC) party, called the revelation "a serious indictment".

"We always knew there was always collaboration between some Western countries and the apartheid regime," he told AFP.

He claimed that though the incident happened decades ago, the CIA was still interfering in South African politics.

"We have recently observed that there are efforts to undermine the democratically elected ANC government," he alleged. "They never stopped operating here."

"It is still happening now -- the CIA is still collaborating with those who want regime change."

Rickard, who was reportedly employed by the CIA until 1978, died in March, two weeks after talking to Irvin in the US.

The CIA declined to comment.