Football's world governing body FIFA have admitted they are investigating whether Russia's entire 23-man 2014 World Cup squad were part of the country's state-supported doping programme and cover-ups.

The bombshell revelation comes after a Mail on Sunday investigation found those 23 players and another 11 footballers are among more than 1,000 'people of interest' to officials charged with getting to the bottom of global sport's biggest scandal of the past decade.

With Russia currently hosting the Confederations Cup — they lost 2-1 to Mexico in Kazan on Saturday night — and one year before they stage the World Cup, these incendiary developments pose further questions about their suitability to host that showpiece.

FIFA are investigating whether Russia's 2014 World Cup squad were part of a state-supported doping programme

FIFA have confirmed knowledge of the allegations against the Russian players, and are in possession of detailed evidence and intelligence.

What action they are taking is unclear but respected anti-doping advocates say FIFA must act — or face derision.

'There is a huge onus on FIFA to reach a sensible conclusion on these matters before the World Cup takes place,' said lawyer Dick Pound, the former head of the World Anti-Doping Agency (WADA) and the longest-serving current member of the International Olympic Committee (IOC).

'It is incumbent on them to say what steps they are taking, what they find, and take whatever action necessary to protect the integrity of sport.

'Even within a governing body with as little credibility remaining as FIFA, if you were a senior official you wouldn't want to be part of a body that ignores this.

'There has been an institutional denial of doping in football for years … I've seen too many presentations by FIFA, straight out of fantasy land, about how they don't have a problem. They absolutely have to take this case seriously.'

The Mail on Sunday's exclusive investigation into the fallout from the Russian doping scandal shows:

Lawyer Dick Pound claims FIFA are in fantasy land if they don't think there is a problem

Hundreds of elite Russian sportspeople suspected of benefiting from a state-backed cheating scheme continue to compete at world level, some not even being scrutinised by their sporting authorities, let alone prosecuted.

The 34 footballers are of interest to the anti-doping authorities because of irregularities with some urine samples — although it is unclear which ones relate to World Cup players — and a concern among investigators that some players at least were being protected from failing tests.

Five of the 23 players tested in 2014 are members of the current Russia squad competing at the Confederations Cup.

Some sports governing bodies have provided breakdowns of cases and action but FIFA declined to do so. A spokesman confirmed, however: 'FIFA is still investigating the allegations made against [Russian] football players.'

Two official reports commissioned by WADA and published last year found at least 1,000 people were assisted by an 'institutionalised manipulation of the doping control process in Russia'.

As an accompanying panel details, the number of individuals being investigated by sport ranges from more than 200 in athletics to double-digit numbers in 13 other sports, and more in others.

The sources of information about some alleged Russian dopers are so sensitive that other cases have not been revealed, even to federations, lest the sources are endangered.

Two former senior Russian anti-doping officials, Vyacheslav Sinev and Nikita Kamaev, both died in mysterious circumstances in close proximity to each other last year.

Russia are currently hosting the Confederations Cup ahead of next year's World Cup

Documents seen by the Mail on Sunday reveal astonishing new details of the doping programme unfolding, including panic among Russian apparatchiks, fully aware of the cheating they were facilitating — from at least 2011 to 2015 — but still dumbfounded by how blatant some sportsmen were being.

The Mail on Sunday's investigation brings the first confirmation that Russia's international football team are implicated — a massive embarrassment to the president of the Russian FA, Vitaly Mutko, the former sports minister named in the WADA reports as playing a key role in the scandal.

He is also the man who led Russia's successful bid to stage the 2018 World Cup. He has always denied any knowledge of, let alone involvement in doping.

FIFA president Gianni Infantino was pictured laughing and smiling with Russian president Vladimir Putin in St Petersburg last weekend.

One source in Moscow says: 'Mutko has kept his job at the FA only after convincing Putin that he has a key relationship with FIFA that needs to be maintained for the World Cup.'

The Mail on Sunday has established that 100 footballers' urine samples are among a batch of around 3,500 'airlifted' from Moscow to Lausanne by WADA two years ago that are waiting to be examined.

The WADA-commissioned investigative team were headed by a Canadian lawyer, Professor Richard McLaren.

They gathered evidence ranging from testimony of key figures involved — including the former head of Moscow's main lab, Grigory Rodchenkov, now under American protective custody in the USA — to spreadsheets of doping schedules, emails and texts.

Russia destroyed masses of evidence when the scam was rumbled. But even amid what was left, sources say there is 'compelling evidence' of possible anti-doping violations in around 600 cases, and 'evidence' in hundreds more.

Dossiers were handed to international federations in December last year, with supplementary materials in May. Some of the information has been placed in the public domain, anonymised, on a dedicated 'Evidence Disclosure Package' (EPD) website.

The Mail on Sunday spent hundreds of hours examining paperwork, cross-checking details. A pattern emerged among footballers, the path of evidence leading back time and again to a list of redacted names, compiled in June 2014.

Could it be Russia's pre-World Cup training camp? We contacted a source in Moscow, who removed themselves from the earshot of others — and bugging devices — and confirmed: 'Yes, World Cup squad.'

FIFA have now confirmed that.

It is understood one issue is whether there is evidence of urine-swapping to ensure a particular batch of samples was clean before the squad departed 'healthy' (as one document says) to the World Cup in Brazil.

One sports administration source suggested maybe some Russian athletes were unknowingly 'kept clean' by the authorities, their urine swapped for pure samples whether they were on doping programmes or not, just to make sure.

Russian FA President Vitaly Mutko has always denied any knowledge of doping

Pound is sceptical that any Russian involved in the state cheating system was naive.

'I compiled my own report at the start of this, into the Russian track and field athletes,' he said.

'What we found was athletes were bringing clean urine to the authorities, which was then frozen, in case a clean sample was needed later. They knew perfectly well what they were doing.'

It remains unknown what happened with Russia's footballers — hence the need for FIFA to investigate thoroughly.

Some records for individual footballers, away from the June 2014 batch, show irregularities in samples from steroids to high testosterone levels.

Innocent explanations are possible, for example via medicines provided legally for some reason.

Correspondence in the EPD shows how even some corrupt officials became concerned at the blatant cheating across many sports.

One email sent on Christmas Day 2013, a few weeks before the 2014 Winter Olympics in Sochi, from a colleague of Rodchenkov to the lab boss, talked of a drug-laden sample of a biathlon competitor containing three banned substances.

'Samples like this should not make it to the laboratory,' it said.

FIFA president Gianni Infantino was pictured laughing and smiling with Russian president Vladimir Putin in St Petersburg last weekend

Rodchenkov played a key role in providing doping products and then covering up positive tests but even he was exasperated at the industrial drug use.

One email he sent said: 'They've completely lost their last bits of conscience.'

Rodchenkov appears to implicate the Russian government in June 2014, when corresponding about a rower with a cocktail of drugs in his system.

He asked a colleague: 'Is rowing one of the ministerial [doping] programmes too?'

The colleague replied that the drug combination was 'well known' in rowing, adding 'but nevertheless, experiments like this must be authorised … and we should be notified [to expect it].'

In August 2014, months after the Sochi Winter Olympics when doped Russians got away with cheating because Rodchenkov and the system 'laundered' their samples, Rodchenkov was staggered at the levels of doping products still used by winter athletes.

The official translation of one email, about a bobsleigh competitor, says: 'Why the f*** are they providing samples! It's a bomb under the lab … I suggest we screw him up to send a message to everyone else. They are taking the p*** now.'

And as late as May 2015, the manipulation was continuing, with a lab worker describing in precise terms how certain tainted samples needed to be artificially diluted to bring high steroid levels within acceptable ranges.

'DON'T use email for stuff like this!' Rodchenkov blasted back in an email. 'Delete everything immediately.'

Pound is sceptical about what will happen next.

The WADA-commissioned investigative team were headed by a Canadian lawyer, Professor Richard McLaren

'My sense is that most international federations are reluctant to dig too deeply,' he says.

'Whether WADA exercise their right to appeal if an IF doesn't act and evidence appears to be there, we'll see whether they have the appetite.'

Even a few successful prosecutions per sport would, de facto, be acknowledgement of an organised system that Russia will eventually be forced to accept.

'Their position is there was never any government programme,' Pound says. 'That's wrong, and misguided.'

Sources say some federations are conflicted due to personal connections to alleged cheats.

One federation known to the Mail on Sunday has close links to an influential (and hitherto untarnished) gold medal winner from Sochi, known to have taken a cocktail of banned drugs, and currently holding prominent office in his sport.

Sources claim some federations have been targeted with bribery attempts not to pursue doping cases.

'There are some federation officials who have been 'sexually compromised', said one source, a reference to the well-established old-style KGB tactic of honey-trapping blackmail targets.