Political leaders in South Africa must "think" before they make statements, which could be "misunderstood", President Jacob Zuma said on SABC radio on Saturday.

Zuma was giving a special public address after Afrikaner Weerstandsbeweging (AWB) leader Eugene Terre'Blanche was murdered on his farm outside Ventersdorp at the age of 69 on Saturday.

"This happening must indeed say to us as leaders we need to think before we make statements in public that might be misunderstood to be encouraging the opposite of what we are trying to do - to build our new nation - irrespective of what quarter they come from, so that no one could attempt to say that what we say is not helping the process of nation-building."

Terre'Blanche was allegedly stabbed and beaten to death on his farm by two employees over a pay dispute between 5pm and 6pm on Saturday. Police arrested two of his employees aged 15 and 21 and seized an iron rod and a panga (machete) that were allegedly used in the murder.

Terre'Blanche's murder has come in the midst of controversy around African National Congress Youth League (ANCYL) president Julius Malema's singing of a traditional ANC struggle song, containing lyrics calling for people to "shoot the boer (white farmer)".

Afrikaans civil organisation, Afriforum was this week successful in a court application to prevent Malema from singing the song.

They claimed that the song incited violence against white farmers in the country.

On Sunday night, Zuma said that calm needed to prevail in South Africa. "All leaders who lead this country, from different political formations and nongovernmental organisations, should unite in the call for calm.

"I know for a fact that those who have been close to Mr. Terre'Blance, they must be feeling a pain, but it is this time that we take our leadership responsibility to make this country unite in calling for a stop of violence," said Zuma.

"Violent crime must be stopped and defeated by all of us." Zuma, who said that Terreblanche's murder was a "sad moment" for the country, termed the act "cowardly".

"I condemn this cowardly act and the murder of Mr Terre'Blanche. It's not acceptable in our society. In due course we will know what is it that led to this terrible action."

He said the news of the murder was shocking.

"It is shocking that a leader of his standing should be murdered by people as it happened. It is even more shocking that people that murdered him was his employees. [That] People that you trust, that you have employed should be the ones that take away your life. This indicate the problem we have in the attitudes and relations among our people."

Zuma said that he had conveyed his condolences to Terre'Blanche's daughter with the hope that she would convey it to her mother. He said he hoped to convey them personally later on Sunday.