One of the remaining two Rivonia trialists has warned the African National Congress (ANC) not to take lightly Ahmed Kathrada's recent criticism of the party.

"It was not that he hated the organisation. He criticised it because he loved it and he was prepared to say where it had gone wrong," Andrew Mlangeni told News24 on Tuesday.

Almost a year ago, Kathrada wrote an open letter to Zuma, calling on him to step down. This was after the Constitutional Court found he failed to uphold the Constitution when he ignored the Public Protector's recommendation that he repay some of the public money used to upgrade his Nkandla home.

"To paraphrase the famous MK slogan of the time: There comes a time in the life of every nation when it must choose to submit or fight. Today I appeal to our president to submit to the will of the people and resign," Kathrada said.

"The organisation should not take his criticism lightly, because many other people are beginning to criticise the ANC, which we love so much.

"His criticism is genuine criticism. Something is wrong and he was saying let us correct our mistakes to lead South Africa correctly," Mlangeni said.

Official memorial

President Jacob Zuma declared a special official memorial for Kathrada. Deputy President Cyril Ramaphosa will lead the send-off of the much-loved stalwart.

Mlangeni said he last visited his friend on March 14, and had been preparing himself mentally and spiritually for his death.

"When I saw him in the hospital, I knew in my heart that sooner or later he was going to leave us."

Mlangeni and Denis Goldberg are the two remaining Rivonia trialists. They were sentenced to life imprisonment alongside the late president Nelson Mandela in 1964.

He praised Kathy, as he was affectionately called, for his dedication to the liberation of SA.

"We have lost a humble man, a person dedicated to the struggle for freedom. Throughout his whole life he was committed to the struggle for freedom, starting with the Transvaal Indian Congress and then the ANC," Mlangeni said.

"We should learn from Kathy humility, respect for people, love for organisation and commitment to fighting for the rights of oppressed people," Mlangeni said.

He sent his condolences to Kathrada's family.