The coach of some of the world’s most famous distance runners was arrested in Spain on Monday in a sting operation that rocked athletics once again.

Jama Aden, coach of poster girl and world-record holder Genzebe Dibaba, was found with EPO and other banned substances in a hotel outside Barcelona.

He was detained by Spanish police along with an unnamed trainer from Morocco as 22 athletes who were also guests at the Sabadell hotel, including Ethiopia’s Dibaba, were drug-tested. The raid came after four weeks of round-the-clock surveillance following a three-year investigation Sportsmail has been working on with the IAAF world governing body since last year.

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Jama Aden (left) and Mo Farah in Ethiopia - Farah distanced himself from the coach on Monday night

Britain’s Mo Farah was distancing himself from Aden and his stable of medal-winning runners who the double Olympic champion has trained alongside in Ethiopia.

There were also questions for UK Athletics about why they allowed one of their most high-profile athletes to be so closely linked to Aden.

Sportsmail can reveal the governing body in the UK rejected Aden, who was based in Sheffield for 17 years with his English wife, for a coaching job in 2006 but still used him as an ‘unofficial facilitator’ for Farah’s high-altitude training camp near Addis Ababa in 2015.

The raid came as Aden and his athletes returned to their four-star hotel at 11am on Monday after a training session. EPO, other unnamed medicines and unlabelled products were found in at least two of four hotel rooms that were searched by Spanish police. The investigation — which has been led by the IAAF along with Interpol and the World Anti-Doping Agency — threatens to blow apart East African distance running.

‘We’re very confident of bringing anti-doping violation charges,’ a member of the IAAF’s anti-doping department told Sportsmail. ‘Jama can be questioned for the next 72 hours by Spanish police. Whether we can charge him will depend on what exactly we have found but if he is charged we will interview him to see if he wishes to divulge any information which can implicate anyone else.’

The IAAF expect the results of the urine and blood tests they took from the athletes, some of whom were not part of Aden’s group, by Friday. Dibaba, who Aden coached to a 1500m world record in Monaco last July, was among those tested. She is favourite to win Olympic gold this summer.

Police guard the entrance to the Arrahona hotel in Sabadell during a doping raid on Monday

‘Dibaba is the distance-running heroine at the minute,’ one prominent athletics figure told Sportsmail. ‘She’s attractive, draws a crowd, waves nicely and sets world records. She’s a ticket-selling dream.’

David Torrence, an American distance runner once coached by Aden, revealed to Sportsmail he was repeatedly encouraged to take injections of ‘vitamins’, but refused. ‘He was like, “Hey David, you should really reconsider taking these vitamin injections, it’s really going to help you”.

‘I was like, “Can I just take it orally, I’ll be more comfortable with some sort of supplement I can take — magnesium, potassium, whatever”, and he’s like, “No, you have to take it with a needle because you get this flush reaction that you can only get with the concentration going directly into you with a syringe”.’

One of Aden’s former athletes, banned for doping last year, alleges the Somalian coach tricked him into using performance-enhancing drugs. Hamza Driouch was considered one of the brightest talents in athletics when he joined Aden’s group aged 14 and for years everything was ‘very normal’, he told Sportsmail from Qatar last November.

But in 2011, the injections began. ‘He would call me into his room — always just me and him — to give me injections of around 5ml three times a week. When I asked him, “What is this good for?” he told me, “This is good for recovery, don’t ask me again if you want to be a good champion. You are like my son”. I trusted him.’

Materials are carried by police officers from the Arrahona hotel and put in a car during the raid

Driouch said Monday was a ‘good day for clean sport.’

Those who dared to speak out against Aden risked aggressive silencing campaigns. The highly regarded American coach John Cook, who was a long-time mentor to Aden, said he received death threats when he raised concerns over the performance of Taoufik Makhloufi, the Algerian trained by Aden who won 1500m gold at London 2012.

Cook told Sportsmail: ‘I suggested I was suspicious. I received death threats. I got phone calls from ambassadors, mostly from the Middle East and Africa, threatening my life.’

It is an uncomfortable association for Farah and comes a year after his coach Alberto Salazar was put under investigation by the US Anti-Doping Agency after allegations in a BBC Panorama documentary that the Cuban-born coach flouted anti-doping rules. In 2015 Aden timed Farah’s training sessions in Ethiopia and the Briton travelled back to his accommodation and dined with Aden’s group. This set-up was put under review by UKA last year after Hamza Driouch was convicted of doping.

When Farah returned to Ethiopia for several weeks this winter he was supervised by UKA’s head coach Neil Black and was pictured with Aden after a training session. British 800m runners Mukhtar Mohammed and Jermaine Mays also regularly train with Aden.

Ethiopia's Genzebe Dibaba celebrates after winning gold in the women's 3000m final at the IAAF World Indoor Championships in Portland in March

‘Jama is a good friend of Mo,’ a top UK coach told Sportsmail, ‘and his athletes are the best so it is a natural fit for him to train with them but Mo should have more sense. He’s distanced himself from Salazar, rightly, to a certain extent after the USADA enquiry. I can’t believe he’s put himself in a position where Jama is pictured next to him.’

A UKA spokesman said: ‘We are always looking at and improving our systems and improving on best practices. A number of changes were made as part of our ongoing reviews, which included making sure our athletes were always supported by performance staff and not left unattended for even the shortest periods during these training camps.

'As is common with athletics, different training groups will be on the same track at the same time – especially in this part of Ethiopia where there is only one track, so sessions inevitably overlap or occur at the same time. Everyone wants a photo with Mo and it isn’t uncommon for other athletes to ask for one. Aden has not coached Mo and is not part of his set-up.’

Police officers stand outside the Arrahona hotel during the doping raid in Sabadell, Spain on Monday

Sportsmail has been co-operating with the IAAF’s investigation into Aden’s group since last November, sharing information about the mechanics behind the alleged doping, including where substances were being stored and by whom. In February we agreed not to run a string of sensational claims from athletics which the IAAF claimed would place the operation ‘at serious risk and be of very serious detriment of the fight against doping in sport.’

An IAAF insider said this raid was the ‘final piece in the puzzle’ after many months of heightened investigation. In July last year Spanish police, acting on behalf of the IAAF, stopped a car containing some of Aden’s athletes travelling between Monaco and their training camp in Font Romeu. It is believed some doping paraphernalia was found.

There is no suggestion Farah, Dibaba, Makhloufi, Mohammed or Mays were involved in any wrongdoing.

The IAAF released a statement on Monday: 'The arrest today of distance running coach Jama Aden, followed a lengthy investigation by the IAAF which began in 2013, working in close cooperation with Interpol, the Spanish authorities including the Spanish National Anti-Doping Agency (AEPSAD), Spanish police and other organisations.

'The IAAF will use all available resources and powers to protect clean athletes and the integrity of our sport. This includes targeting and investigating individuals and coaches who are intent on exploiting athletes and promoting the use of prohibited substances.