TikTok, the popular Chinese-owned social network, instructs its moderators to censor videos that mention Tiananmen Square, Tibetan independence, or the banned religious group Falun Gong, according to leaked documents detailing the site’s moderation guidelines.

The documents, revealed by the Guardian for the first time, lay out how ByteDance, the Beijing-headquartered technology company that owns TikTok, is advancing Chinese foreign policy aims abroad through the app.

The revelations come amid rising suspicion that discussion of the Hong Kong protests on TikTok is being censored for political reasons: a Washington Post report earlier this month noted that a search on the site for the city-state revealed “barely a hint of unrest in sight”.

The guidelines divide banned material into two categories: some content is marked as a “violation”, which sees it deleted from the site entirely, and can lead to a user being banned from the service. But lesser infringements are marked as “visible to self”, which leaves the content up but limits its distribution through TikTok’s algorithmically-curated feed.

Q&A What is TikTok? Show Hide TikTok is a video-sharing app which has become phenomenally popular with teenagers. Users film themselves in 15-second clips, typically set to music, and upload them to be viewed by followers and strangers alike. It has been the No 1 app on the worldwide App Store for five consecutive quarters, with an estimated 500 million users worldwide. Owned by Chinese startup ByteDance, the app as it is today is a merger of the original TikTok, which was launched internationally in September 2017, and the viral sensation Musical.ly. The latter had already become one of the most popular social media platforms for UK and US teenagers by the time it was purchased by ByteDance in November 2017. The merger meant TikTok ended up on the smartphones of more than 60 million users overnight. Bytedance has a valuation of $75bn (£60bn), based primarily on the extraordinary growth of TikTok and its Chinese equivalent, Douyin. Lil Nas X found fame overnight when his track Old Town Road was used extensively on 15-second clips on the social network. That enthusiasm took the artist to a record-breaking run at the top of the US Billboard Hot 100 chart. However, Bytedance was fined a record $5.7m in the US for illegally collecting personal information from children under 13, and has been under investigation in the UK for how it handles the personal data of its young users, and whether it prioritises the safety of children on its social network. Alex Hern, UK technology editor

This latter enforcement technique means that it can be unclear to users whether they have posted infringing content, or if their post simply has not been deemed compelling enough to be shared widely by the notoriously unpredictable algorithm.

The bulk of the guidelines covering China are contained in a section governing “hate speech and religion”.

In every case, they are placed in a context designed to make the rules seem general purpose, rather than specific exceptions. A ban on criticism of China’s socialist system, for instance, comes under a general ban of “criticism/attack towards policies, social rules of any country, such as constitutional monarchy, monarchy, parliamentary system, separation of powers, socialism system, etc”.

Another ban covers “demonisation or distortion of local or other countries’ history such as May 1998 riots of Indonesia, Cambodian genocide, Tiananmen Square incidents”.

A more general purpose rule bans “highly controversial topics, such as separatism, religion sects conflicts, conflicts between ethnic groups, for instance exaggerating the Islamic sects conflicts, inciting the independence of Northern Ireland, Republic of Chechnya, Tibet and Taiwan and exaggerating the ethnic conflict between black and white”.

All the above violations result in posts being marked “visible to self”. But posts promoting Falun Gong are marked as a “violation”, since the organisation is categorised as a “group promoting suicide”, alongside the Aum cult that used sarin to launch terrorist attacks on the Tokyo Metro in 1995 and “Momo group”, a hoax conspiracy that went viral earlier this year.

Falun Gong has been suppressed by Beijing since 1999, but an incident in 2001 when five people self-immolated in Tiananmen Square has been used to justify moves against the group since.

Ofcom investigates CGTN over coverage of Hong Kong protests Read more

Odd rules can be found elsewhere in the guidelines. The service’s policies regarding what it describes as “underage pornography”, for instance, explicitly detail four categories of underage users: an infant or toddler, under one year old; a child, 1-8 years old; an adolescent; and a minor, any person less than 18 years old. However, if it is “unclear” whether a user is under 18, the guidelines explicitly recommend that moderators “treat [the subject] as an adult”.

The service also bans a specific list of 20 “foreign leaders or sensitive figures” including Kim Jong-il, Kim Il-sung, Mahatma Gandhi, Vladimir Putin, Donald Trump, Barack Obama, Kim Jong-un, Shinzo Abe, Park Geun-Hee, Joko Widodo and Narendra Modi. Notably absent from the list is Xi Jinping, the Chinese chairman.

Bytedance said the version of the documents the Guardian has seen was retired in May, before the current protests in Hong Kong began, and that the current guidelines do not reference specific countries or issues.

“In TikTok’s early days we took a blunt approach to minimising conflict on the platform, and our moderation guidelines allowed penalties to be given for things like content that promoted conflict, such as between religious sects or ethnic groups, spanning a number of regions around the world,” the company said. “As TikTok began to take off globally last year, we recognised that this was not the correct approach, and began working to empower local teams that have a nuanced understanding of each market. As we’ve grown we’ve implemented this localised approach across everything from product, to team, to policy development.

“The old guidelines in question are outdated and no longer in use. Today we take localised approaches, including local moderators, local content and moderation policies, local refinement of global policies, and more. We also consult with a number of independent local committees and are working to scale this at a global level, including forming an independent committee of leading industry organisations and experts to continually assess these policies.

“We also understand the need to be more transparent in communicating the policies that we develop and enforce to maintain a safe and positive app environment. Users gravitate to TikTok because it provides an app experience that fosters their creativity, and we are committed to supporting that across our teams, product, policies, and the way in which we openly communicate with our community.”

The service was launched in 2017, shortly before being merged with an American company, Musical.ly, that ByteDance purchased for a reported $1bn (£800m) in order to boost the growth of the app.

A similar, China-only app, Douyin, launched in 2016, and grew to count one in 10 Chinese people as users by the end of 2017.

TikTok was the most-downloaded item on the iOS App Store worldwide in the first half of 2018, and has remained hugely popular, particularly among its core user base of under-25s, ever since. But that popularity has been expensive: ByteDance has spent a reported $1bn on Facebook advertisements to keep growth high.