Ventersdorp - A South African white supremacist group whose leader was killed, warned other countries on Sunday to avoid sending their football teams to the World Cup in "a land of murder".
Andre Visagie, a senior member of the Afrikaner Weerstandsbeweging (AWB), said the slaying of leader Eugene Terre'Blanche "is a declaration of war" by blacks against whites in South Africa.
Visagie said the AWB would respond by telling countries to reconsider participating at the World Cup, which begins on June 11.
"We're going to warn those nations they are sending their soccer teams to a land of murder," Visagie said. "Don't do that if you don't have sufficient protection for them."
Visagie vowed to avenge the death of Terre'Blanche, but did not specify what form the vengeance would take.
President Jacob Zuma appealed for calm following "this terrible deed".
In a statement, he asked "South Africans not to allow agent provocateurs to take advantage of this situation by inciting or fuelling racial hatred."
Police said Terre'Blanche was bludgeoned to death in his bed on Saturday by two of his farm workers in an apparent wage dispute.
South Africa has been under constant scrutiny ahead of hosting the world's biggest football tournament because of its high rate of violent crime.
The country's ruling ANC party criticised the AWB for advising teams against playing at the World Cup.
"We don't think that it's the right thing to do," ANC spokesperson Jackson Mthembu told The Associated Press.
"This is a World Cup for all of us, not only black people of this country. And we have to give all the support we can for the World Cup to happen here in South Africa.
"We think our compatriots in the AWB should do the same as other patriotic South Africans."