WikiLeaks founder Julian Assange’s fiancee has appealed for him to be freed to restore the public’s faith in “mature democracy”.

Stella Moris penned an opinion piece recounting her vivid childhood memories of Botswana during South Africa’s deadly raid on the capital Gaborone in June 1985.

The 37-year-old says half of the 12 people killed by Apartheid government forces were civilian activists and not African National Congress fighters.

“I have absorbed my parents’ vivid memories of the raid,” Ms Moris wrote in Spanish newspaper El Pais on Friday.

“If that terrible night shaped my perspective of the world, the incarceration of the father of my children will surely mark theirs.”

She then detailed the harassment they faced when Assange was living the Ecuadorian embassy.

Ms Moris says a Spanish security firm spied on them and tried to steal their son Gabriel’s nappy for a paternity test.

The same firm also had plans to poison or abduct Assange, she says.

“None of this information is surprising to me but as a parent I ponder how to manage it,” she wrote.

“I want our children to grow up with the clarity of conviction that I had as a little girl. Peril lay beyond the South African border. I want them to believe that inequitable treatment is not tolerated in mature democracies.”

Ms Moris said if she and her sons are targets of harassment then nothing is off-limits.

She accused US Secretary of State Mike Pompeo of ordering the theft of her son’s nappy.

She said Pompeo had also in April threatened the families of International Criminal Court Lawyers who investigating alleged US war crimes in Afghanistan.

“The same crimes that Julian exposed through WikiLeaks, and which the US wants to imprison him over,” she said.

“Julian needs to be released now. For him, for our family, and for the society we all want our children to grow up in.”

Assange’s lawyers are expected to agree to a new date for his extradition hearing at Westminster Magistrates Court on Monday.

The Australian faces 17 charges of violating the US Espionage Act and one of conspiring to commit computer intrusion.

He’s accused of publishing thousands of secret US diplomatic and military files, some of which revealed alleged war crimes in Iraq and Afghanistan.

The charges carry a total of 175 years’ imprisonment.

-AAP