Transgender women participating in female sports have been the subject of news stories and intense debate for a number of years.

But while these concerns would seemingly not apply to chess - a sport in which mental fitness is more relevant than supposed physical differences - the International Chess Federation (Fide) has chosen to ban trans women from female-only events.

Why has this happened? It's a complicated picture involving Russia, anonymous complaints and the sport's lone top-level trans female player.

What are the new rules in chess?

Fide introduced a ban on trans women competing in female-only events. Chess has male-only, female-only and mixed-gender competitions.

According to Fide, gender reassignment "has a significant impact on a player's status and future eligibility for tournaments".

"In the event that the gender was changed from a male to a female, the player has no right to participate in official Fide events for women until a further decision is made," its statement reads.

"Such decisions should be based on further analysis and shall be taken by the Fide Council at the earliest possible time, but not longer than within a two-year period."

When asked by BBC Sport for an explanation as to what this further analysis entailed, Fide said it planned to do a "comprehensive analysis to understand the impact of various factors, including but not limited to, the role of testosterone levels, on chess performance".

Fide also said any titles won by transgender men in the female category would no longer stand. Any titles won in male events by trans women, before gender reassignment and a move into different gender category, still stand.

Asked by BBC Sport if there had been any cases of this happening, Fide confirmed "there have been no registered instances of women's titles being revoked as a result of gender changes".

The rules give Fide "the right to inform the organisers [of competitions] and other relevant parties on the gender change" and "to make an appropriate mark in the players' database and/or use other measures to inform organisers on a player being transgender, to prevent them from possible illegitimate enrolments in tournaments".

A spokesperson for the organisation told BBC Sport "the absence of such regulations created ambiguity and an established procedure was needed to ensure transgender players are properly represented in Fide's register".

It also said "these limitations apply to a very limited number of tournaments, specifically official Fide women's events" and that "approximately 99% of all national, regional, and international open and women events remain open to transgender players".

What has been the reaction in the world of chess?

The rules have been heavily criticised by notable female chess players including Jennifer Shahade - Fide grandmaster and two-time US women's champion.

"The rules have had a really upsetting effect on the chess community," Shahade told BBC Sport. "They seem very cruel.

"The practical ramifications, I'm not sure of yet, but they will have an effect on the LGBT community - people saying even if they are unlikely to qualify for events, it makes them want to play chess less.

"All these requirements around ID... a two-year decision period is a long time - if you are at the peak of your sport it is an eternity.

"The reason these policies come out is that people really believe players will pretend to be women to win events and take prize money. But a lot of these policies have been in effect for 10 years. Why has it not happened yet?

"People really are paranoid that it will ruin women's chess, that it will dissolve and sponsors will leave. The antidote is talking to actual trans players."

Yosha Iglesias was granted the rank of Fide master in 2019 and, in 5,425th place, is the highest-ranked female player who is out as transgender. She says Fide did not consult her or any other trans people associated with chess that she has spoken to.

"They have self-attributed the right to out any trans player at any time to any organisation," she tells BBC Sport. "I don't really care because I'm out, but it could put lives in danger.

"If a trans player was stealth [had not disclosed their trans identity] and playing in a country where being LGBT is illegal or dangerous, if Fide decide to out you, it could be life-threatening."

Chess federations have also criticised the move.

"The new Fide rules are incompatible with English law, particularly with regard to the release of personal data," "We cannot see the point of the two-year suspension of the right to participate in women-only competitions, which we view as discriminatory."

United States Chess Federation (USCF) senior director of strategic communication Daniel Lucas told "While we do take Fide policies into consideration, we independently establish our own policies and procedures."

The starkest criticism came from Jean-Baptiste Mullon - vice-president of French Chess Federation (FFE) - who told "This Fide press release is a poorly written and even transphobic text."

'I have all this weight on my shoulders'

Iglesias - the only transgender player currently ranked as a master by Fide - was flying to Albania for her first chess tournament outside western Europe since coming out in 2021 when she first heard about an issue.

"On the plane to the Euro Chess Union tournament, an official told me that one grandmaster wrote an official letter demanding that I should be banned," Iglesias said.

While individual national committees can have their own policies on gender inclusion for tournaments they run, this ban would apply for events organised by Fide, including the World Championship, European Championship and most of chess' prestigious competitions.

This has left Iglesias and other trans players feeling they have no place in the sport.

"They met and decided to include me. Some officials in Eastern Europe were pro-ban but most were against," said the French player, referring to the Albanian tournament organising committee's decision, which came before the letter calling for her to be excluded.

"Still, it's scary. Sometimes I feel like I have this weight on my shoulders because these laws are made for all trans players, but I am the only one. I always have to be perfect.

"That letter, was it against me or just against trans players?"

What support has there been for the new regulations?

While there has been criticism of the ruling from players around the world, in Russia they have been welcomed.

"There are no reasons at all for transgender people to compete among other athletes based on common grounds," Dmitry Svishchev - chairman of the Russian State Duma Committee on Physical Culture and Sports - told Russian news agency

"Besides a possible physical advantage there are moral and ethical aspects, which may become unbearable for an ordinary athlete."

There has also been support outside Russia from those who feel transgender women could have a biological advantage.

Harvard evolutionary biologist Dr Carole Hooven wrote on that "men have a large and consistent advantage over women in spatial ability, on which chess relies to a large extent", although evidence to support this is "mixed, and no single trait (other than practice) strongly predicts success among the top-rated players".

Fide says it will ensure all players' personal information is protected, and that the regulations will not out any trans player or put them in danger.

"Fide will facilitate the registration of gender changes based on national legislation, eliminating the need for additional procedures," a spokesperson told BBC Sport.

"Regarding the right of Fide to make an appropriate mark about gender transition in the players' database, Fide does not plan to apply such marks in the database or do any other actions that could be harmful or dangerous for players.

"Previously, Fide had no option at all to step in and make such amendments to the directory if the national federation refused to do so for a player. Now players have an opportunity to request changes being made directly by Fide, and thus transgender players' rights to self-identify will be secured."

How much influence has Russia had regarding these new regulations?

Arkady Dvorkovich, who served as a Russian deputy prime minister between 2012 and 2018 under the presidency of Vladimir Putin, has been the president of Fide since October 2018.

Putin's governments have introduced a series of anti-LGBTQ+ laws while he has been in office, including the "gay propaganda" law in 2013 during Dvorkovich's time in government. That banned promotion of homosexuality among people under 18. Russia also introduced a ban on gender-affirming surgeries for trans people in July this year.

According to Iglesias, the Russian influence on chess is felt heavily through these new laws.

"I am certain there is no coincidence the Fide regulations have been published just after Russia put in place one of the most horrifying anti-trans laws," she said.

"It's also meaningful they did not consult any trans players. They knew what they wanted."

Fide denied that personal bias or political interference had played any role in their new regulations.

"Fide developed these regulations after consulting the guidelines of the IOC [International Olympic Committee] and other sports organisations. We also considered the practices of Fide national federations, and members of relevant Fide commissions provided their input before the council adopted the regulations," a spokesperson said.

"Fide's strategic and oversight body with law-making functions and decisions are made by voting majority - and not the president of Fide.

"Our goal is to provide every person with an opportunity to play chess, with this being fair to everyone else by making the rules clear.

"Work on the transgender policy has been going on for some time and a first version was discussed earlier this year by Fide. We understand the sensitivity of this issue and aim to approach it carefully, without bias."

What is the next move?

Iglesias says she was moved to tears and "so grateful" for the French Chess Federation's support.

As a result, she is doing her best to remain hopeful about the future, while aware her time in elite chess could be shortened.

"There is so much uncertainty, it is hard to make a prediction," she said. "In France, that sport categories should be based on assigned sex at birth. If that happened, I could no longer play as a woman in France.

"You see similar things happening - in the UK and USA too.

"I'm glad I can be like a mother to young trans players. When I was young, I had no-one to look up to, but it's better now than not so long ago."