WikiLeaks founder Julian Assange will appear in a London court on Tuesday (tonight NZT), according to reports.

It will be the 39-year-old Australian's second attempt to win bail after he was arrested over allegations of sex crimes in Sweden, reports AFP.

He was detained a week ago under an international warrant sent out by Sweden, shortly after his whistle-blowing website started releasing tens of thousands of leaked US diplomatic cables, in a move that has infuriated Washington.

At a hearing last week, Assange was refused jailed as he was deemed a flight risk.

Assange's supporters are expected to protest outside the City of Westminster Magistrates Court.

Meanwhile, Assange has issued a plea from jail for his supporters to keep fighting, accusing Visa, Mastercard and Paypal of being instruments of US foreign policy.

In a statement provided to the Sunshine Coast Daily via his Australian mother, Julian Assange said he was determined to fight for the future of WikiLeaks.

"My convictions are unfaltering. I remain true to the ideals I have always expressed," he said from Wandsworth Prison in London.

"These circumstances shall not shake them. If anything, this process has increased my determination that they are true and correct.

"We now know that Visa, Mastercard and Paypal are instruments of US foreign policy. It's not something we knew before.

"I am calling on the world to protect my work and my people from these illegal and immoral acts."

Julian Assange's mother Christine, who lives on the Sunshine Coast in Queensland, has flown to London to visit his son and support him in his bail hearing, expected tonight (NZT).

Mrs Assange was not able to see her son face-to-face on Monday but a 10-minute phone call reunited the duo.

It was the first time the Noosa woman spoke to her son since he was arrested.

Mr Assange told his mum there were CCTV cameras monitoring his cell because of fears he could be assassinated for his role in releasing 250,000 confidential US government documents.

- Sunshine Coast Daily and NZ Herald staff