Four staff of a Chinese media outlet that carried an anonymous letter calling on President Xi Jinping to resign have been missing for over a week, a colleague said Thursday.

A letter appeared on the Wujie News website earlier this month accusing Xi of a litany of policy mistakes and asking him to step down for the good of the country, before it was deleted.

Media criticism of top leaders is almost unknown in China, where the press is strictly controlled by the ruling Communist Party.

Four staff including CEO Ouyang Hongliang and managing editor Huang Zhijie have been "out of contact" since last week, a reporter at the magazine who asked not to be named told AFP.

"I think they are assisting an investigation," said the staffer, adding that the media outlet may be shut down, although the letter's appearance was probably the result of a "hacking attack".

A Chinese journalist, Jia Jia, was held last week at Beijing airport while on his way to Hong Kong, with rights groups linking his detention to an alleged attempt to warn Wujie's CEO about the letter.

But his lawyer has said that his detention may not be connected to the document.

Wujie has not published any original articles on its website since Wednesday last week, and has not updated an account on the Wechat social media platform since Friday.

Xi has tightened already strict controls on the media since coming to power in 2012, and recently urged state-run outlets to "reflect the will of the party".

- 'Personal safety' -

Mainland Chinese media coverage of Xi is typically limited to accounts of meetings or speeches, or gushing with praise.

He has presided over a slowdown in economic growth and a clampdown on civil society that has seen hundreds of people arrested.

The letter, seen by AFP in a cached form, berated him for centralising authority, mishandling the economy and tightening ideological controls.

"Due to your gathering of all power into your own hands and making decisions directly, we are now facing unprecedented problems and crises in all political, economic, ideological, and cultural spheres," it said.

Signed "Loyal Communist Party Members", it added: "For the Party cause, for the long-term peace and stability of the country, and for your own personal safety and that of your family, we ask you to resign from all positions of Party and state leadership."

Wujie -- known as Watching in English -- was founded in 2015 with funding from Internet giant Alibaba, as well as the provincial government of Xinjiang in China's northwest.

It is based in Beijing. Police in China's capital did not answer a phone call asking for comment.

Hong Kong newspaper Apple Daily on Thursday first reported that four staff were missing and added that the outlet was "facing closure".

It earlier reported the letter had appeared as a result of hacking, citing an insider as saying: "Wujie is not so stupid as to mess around in that way."

Drugmaker Novartis settles with US over China bribe claims
Zurich (AFP) March 24, 2016 - Swiss drugmaker Novartis said Thursday it had reached a deal with US authorities to pay $25 million (22.4 million euros) to settle claims that its Chinese units bribed healthcare professionals to boost sales, including with family trips to Niagara Falls.

The drug giant agreed to pay the hefty fine "without admitting or denying" guilt, according to documents published by the US Securities and Exchange Commission (SEC).

According to the SEC findings, Novartis's China-based units had between 2009 and 2013 "provided things of value" mainly to doctors and other healthcare professionals.

"These payments took varied forms and were intended to ... increase sales of Novartis pharmaceutical products," said an SEC document filed late Wednesday.

The market regulator said healthcare providers were for instance invited on expensive trips, which in many cases "did not include an educational purpose or the scientific/educational components were minimal in comparison to the sightseeing or recreational activities."

In 2009, Novartis subsidiary Sandoz China for instance paid for 25 healthcare workers to take part in a surgical conference in Chicago, inviting along their spouses and taking the group on an excursion to the Niagara Falls. Each participant also received $150 in pocket money, the SEC document said.

Employees and managers at the involved units had tried to "conceal the true nature of the transactions", by for instance "improperly recording payments as legitimate expenses" for things like travel, entertainment, conferences and medical studies.

Novartis, which is listed on the New York Stock Exchange, thus stands accused of breaching the US Securities Exchange Act by not keeping accurate books and failing to maintain a sufficient system of internal accounting controls."

But the SEC noted that Novartis had cooperated with its investigation and opened its own internal probe, letting go or disciplining employees found at fault.

It has also since put stepped up its control mechanisms, the SEC said.

The pharmaceutical giant itself acknowledged the deal with the SEC, but stressed that the incidents in question "largely pre-date many of the compliance-related measures introduced by Novartis across its global organisation in recent years."

"We believe these measures, which we review and update on an ongoing basis, address the issues raised by the SEC," Novartis spokesman Eric Althoff told AFP.