President Thabo Mbeki on Friday accused special investigating unit head Judge Willem Heath of "touting" for work with an incomprehensible "level of desperation".

In a letter explaining to Heath why his unit was excluded from the probe into South Africa's R43-billion arms deal, Mbeki also rebuked the judge for apparently not trusting the government.

The letter was released after a media briefing by Director-General in the Presidency Frank Chikane to announce that the Heath unit would not be involved in the arms acquisition probe.

Mbeki told Heath that he (the president) had been led to believe that the judge knew of no prima facie evidence of wrongdoing in the arms procurement process.

Members of Heath's own unit were actually under the impression that the judge had indeed told Mbeki there was no reason for the unit to join the arms deal probe.

Mbeki wrote: "This would have been the correct thing for you to do, which you did not do. Instead you embarked on an unseemly campaign to 'tout' for work, with a level of desperation I am still trying to understand."

The president also rebuffed Heath for suggesting that information he had on the arms deal was safer in his hands than in those of the government.

Mbeki quoted a letter he received from Heath on January 16, saying: "Should the information received by the unit be disclosed (to the government) ... it could possibly jepodise (sic) the investigation as well as the lives of the informants...

"In addition to this, should this information become public knowledge, it could lead to a cover-up," Heath wrote to Mbeki.

In reaction, Mbeki asked in his letter how a government that appointed the Heath unit could be prone to cover-ups.

He added: "Worse than this, you charge that once the information you have was given to the government, in this case the president, the lives of the informants might be jeopardised!

"These are very serious charges which you will have to substantiate," Mbeki told Heath.

Chika said the letter was sent to Heath earlier in the day.

With acknowledgment to Sapa and Independent Online.