DA spokeswoman Dene Smuts described the painting as "iconic" and a brilliant work of political satire.

"South Africa has been descending for some time into a censorious mind-set that is taking us further and further away from the free speech which is fundamental to our democracy," she said.

"If the president feels that his dignity has been impugned, he should sue Murray for damages as he is suing the cartoonist Zapiro."

Applying to court to shut down the exhibition was unjustifiable censorship, she said.

The Moral Regeneration Movement said it had noted "with grave concern" the public debate surrounding the artwork.

"This portrait has evoked a reaction we have not witnessed in years. Many people have been shocked, angered and outraged by what is perceived as an assault on the personal integrity of President Jacob Zuma," said spokesman Smangaliso Mkhatshwa in a statement.

Implied within the right to freedom of speech and expression was the obligation to respect the rights of others, he said, adding: "Not all legally correct actions are morally acceptable."

The least one could do was to respect the office of the president, said Mkhatshwa.

He said artists should understand that culture and social traditions played an important role in understanding and appreciating their art. African culture accorded special respect for leaders.

"Could it be that the Brett Murray saga is a wake-up call to black people to take their culture seriously?" he asked

"Whilst we have the numbers, we have allowed the culture of the minorities to set the national culture agenda."

Nevertheless, the MRM did not excuse the actions of those who defaced the portrait, Mkhatswa said.

The Azanian People's Organisation (Azapo) said it did not condone the painting, but found its defacing repugnant.

"We call on law enforcement agencies to act swiftly on those who have allegedly defaced the painting in the Goodman Gallery this morning in Johannesburg," said deputy spokesman Funani ka Ntontela.

"We cannot afford to go back to the old ways where members and supporters of the ANC are not happy with their political opponents resort to criminality."

The Freedom of Expression institute (FXI) said it supported the Goodman Gallery in refusing to remove the picture.

"During the apartheid era, Michaelangelo's statue of David caused a controversy when displayed in a shop window and there were calls for David's nakedness to be covered by a figleaf," it said.

The fact that the painting annoys or offends some people was no reason to seek to remove it.

The test of a country's integrity was its tolerance of expression which caused offence or anger, the institute said.

"We are horrified by the possibility that artwork might not be displayed in a gallery because it causes discomfit in the ruling party."

While it was healthy to debate tolerance, culture, race and repression, the debate had sometimes "taken on a racial tinge".

The FXI said it hoped the courts would defend the artist's right to free expression and the right of creative workers to provoke discussions of this sort.

"We urge the ANC to criticise, even to condemn the work if they wish, to engage in the issues it raises, but not pursue charges or court action which will amount to a bid to censor."

However, different standards applied to media which had reproduced the painting, because of the sensitivity of certain audiences.

"More care has to be exercised where a publication is a newspaper entering homes where young children are present," the FXI said, calling for skilful treatment from editors.

The institute spoke out strongly against a church leader who called for the artist to be banned and stoned.

"The intolerance of such a statement is reminiscent of the worst of apartheid, and the threat of violence totally inappropriate in a constitutional democracy," it said.

The ANC said that while it could not condone any action which was not legal, it equally did not condone the assault of a suspect who was black.

"It is very contrasting and concerning that another suspect, who happens to be a white South African, was not assaulted but was treated with dignity as he was arrested," the party said in a statement.

"Perhaps it is this type of behaviour on the part of Goodman Gallery and its security that might need to be further explained."

The party said the indecency, disrespect and indignity characteristic of the painting had the potential to reverse the healing of wounds inflicted by apartheid and colonialism.

Three people were being held on Tuesday for alleged offences relating to the painting.

Two of them allegedly defaced the picture with red and black paint, obscuring the face and waist of the figure.

A third was arrested for apparently trying to spray the word "respect" on a wall of the Goodman Gallery.

Colonel Vishnu Naidoo confirmed the arrests.

"The two men, 58 and 25 years of age, allegedly made crosses with red paint and smeared black paint respectively on the portrait."

Earlier, the gallery's attorney said the second person was believed to be a 15-year-old.

The arrests came within an hour of the High Court in Johannesburg setting down an application by the ANC to have the painting removed from the gallery for hearing by a full Bench on Thursday morning.

The Film and Publication Board will take submissions on Tuesday night from parties, including the gallery, as it reacts to complaints and decides whether the painting should be classified.

Spokesman for the board, Prince Mlimandlela Ndamase, said it would go ahead in spite of Tuesday's turn of events, because images of the original picture were still widely available on the internet.