Justice and Correctional Services Minister Michael Masutha says he cannot accede to a Democratic Alliance (DA) request to pressure the National Prosecuting Authority (NPA) into probing Nkandla.

Masutha was briefing the media on Thursday ahead of his department's budget vote in Parliament, and said DA leader Mmusi Maimane's request was asking him to interfere with the NPA's independence.

"This request is oblivious of the fact that, though I am enjoyed by the Constitution to exercise final responsibility over the NPA... this does not extend to interfering with the independence of the NPA's discretion," he said.

"Shaun Abrahams is here and can confirm with you that, where necessary, I receive briefings on matters, and he asks questions, but at no stage have I given the NPA instructions to prosecute or not prosecute and when to do so."

Maimane on Monday wrote to the National Director of Public Prosecutions Abrahams asking him to furnish them with a decision on whether to prosecute or not prosecute President Jacob Zuma over security upgrades to his homestead.

According to Maimane, citing Police Minister Fikile Mbalula, the case docket was completed in August 2015 already, and simply awaits a decision from Abrahams.

Acting special director of public prosecutions Advocate M Govender responded, and said further investigation was required.

"This is completely unacceptable and smacks of a justice system using every stalling tactic in the book to avoid prosecuting Jacob Zuma for his unlawful actions," Maimane had said.

"This matter is straightforward. An investigation has been concluded, and the docket has been sent to the NPA. The role of the NPA is simple – it must decide to either prosecute Jacob Zuma or not prosecute Jacob Zuma."

Abrahams, who was present in the auditorium on Thursday, did not comment on Maimane's request.