South African police on Monday said they had arrested four armed right-wing extremists suspected of planning attacks, amid claims that an ANC leadership meeting may have been targeted.
Four men, aged 40-50 years old, were arrested on Sunday, "believed to be right-wing extremists" and "suspected of acts of terrorism," according to Free State police spokesperson Brigadier Billy Jones.
"Their premises were searched and evidence supporting the investigation was seized."
The arrests came after a nearly two-year nationwide investigation, Jones told AFP.
But there were conflicting reports about what the suspects' target or targets may have been, with ANC saying its party conference may have been in the firing line.
Delegates at the Mangaung meeting include President Jacob Zuma and most of the South African government.
Jones denied suggestions the meeting was under threat.
"We are not linking this to the ANC conference. The investigation is taking place at several points across the country," Jones said.
"Four people were arrested, not linked to the conference at all."
National police spokesperson Phuti Setati confirmed that account of events.
But ANC spokesperson Keith Khoza said the party had been given a preliminary report that the men may have been on route to blow up the conference venue.
"We are still waiting for verification of the facts and as to who are these people. Why did they want to do that and how they were going to do that," he told AFP.
Security has been extremely tight around the conference, with barbed wire thrown up around a perimeter guarded by armed police.
Only a few pre-screened vehicles are allowed to enter what is normally the campus of the University of the Free State.
"You've got in here the president and the deputy president of the country. You've got the entire cabinet, the entire top leadership of the ANC nationally and you have diplomats, foreign delegates and you've got 4500 delegates.
"And that calls for maximum security because if anything were to happen you'd have a huge impact on the country and the government," Khoza said.
"The police are currently handling the whole matter so we'll be advised by the police in due course about the plot, if there is one, and who these people are," said Khoza.
Francois Cloete, national secretary of the Federal Freedom Party, told AFP that at least two of the men arrested were members of his party, which backs a federal South Africa with self-governing white regions.
"According to our information, two people were arrested, in Naboomspruit (Mookgophong) in Limpopo province," he said.
"We don't associate at all with acts of terror. Our mission is self-determination through international laws."
"The FVP is a political party, not a military organisation," he added using the group's Afrikaans acronym.
Since the fall of the white-minority apartheid government in 1994, numerous right-wing groups have turned to violence.
In August, 20 people were convicted of high treason in connection with a plot to kill Nelson Mandela and drive blacks out of the country.
The "Boeremag" organisation had planned a right-wing coup in 2002 to overthrow the post-apartheid government.
Dozens of people were injured and one person killed in blasts that shook the Johannesburg township of Soweto in October 2002.
South Africa's opposition Democratic Alliance condemned the alleged plot.
"It appears some on the lunatic fringe of our politics still do not respect the rights of all parties to exist. They must face the full force of the law."
The four will appear in a Bloemfontein court on Wednesday on high treason and terrorism charges.