HONG KONG (AFP) - A top aide to Hong Kong pro-democracy media tycoon Jimmy Lai has stepped down after admitting he helped fund a contentious report alleging links between former US vice-president Joe Biden's son and China, but insisted Sunday (Nov 1) his boss had no knowledge of it.

The 64-page document by a fictitious author, which was circulated online and seized on by US President Donald Trump's supporters, alleges business connections between Biden's troubled son Hunter and China.

But investigations in recent days have raised questions about its veracity and how it was compiled.

In a series of tweets over the weekend Lai said senior aide Mark Simon, a vocal critic of Biden, had "worked with the project".

"Mark used my private company's money to reimburse for the research he requested. It's only US$10,000 (S$13,700) so he didn't have to have my approval," Lai wrote.

"I know it is hard for anyone to believe that I didn't know about it and my integrity is damaged," he added.

Simon resigned from Apple Daily over the weekend.

In e-mails to AFP on Sunday, Simon said he acted in his own capacity in paying for some of the research that ended up in the dossier.

"Apple Daily had nothing to do with the report and certainly Mr Lai has nothing to do with it," he said.

"All were completely unaware of me helping out with expenses of research."

Fabricated author

On Friday, NBC published an investigation saying the 64-page dossier had "questionable authorship and anonymous sourcing".

The investigation found the listed author, a supposed Swiss security analyst called Martin Aspen, was a fabricated identity and that his picture had been created using software.

According to NBC, blogger and academic Christopher Balding, a former associate professor at Fulbright University Vietnam, said he had contributed to the report and admitted Aspen did not exist.

He said the report was was "commissioned by Apple Daily", Lai's staunchly pro-democracy and anti-Beijing newspaper in Hong Kong and Taiwan.

The paper denied that characterisation, as did Simon.

"I nor anyone at Apple did anything in terms of research or writing, just no role whatsoever. All arms length," he said.

"$10k is well within my discretion, but putting Apple people and Jimmy in the firing line was wrong. I was far too casual with using Apple Daily name, I abused the trust I have been given," he added, explaining his decision to resign.

Lai, 71, has long been a thorn in the side of Beijing and has spoken favourably of Trump's willingness to confront China - the only major Hong Kong tycoon willing to do so publicly.

His Apple Daily newspapers and Next Magazine are unashamedly pro-democracy and he is routinely vilified by China's state media.

In Hong Kong, Apple Daily has the highest circulation.

Lai was one of the first people to be arrested under a new national security law that Beijing imposed on Hong Kong in June following last year's huge and often violent pro-democracy protests.

Apple Daily's newsroom was raided by more than 200 police officers and authorities accuse Lai of "colluding with foreign forces" and money laundering.

The investigation is ongoing but Lai has said he fears authorities are trying to shut down a critical voice in the restless city.

Apple Daily's Taiwan edition published two articles recently on Hunter Biden and his ties to a Taiwanese businessman with links to mainland China.

"I think Chris made a mistake in going cloak and dagger," Simon said. "But our Taiwan stories that used the data remain solid. Our Taiwan stories that used the data remain solid," he added.