Somalian coach Jama Aden and a Moroccan physio were arrested at their hotel in Sabadell, 20 miles north of Barcelona, and taken into custody.
The Spanish anti-doping agency (AEPSAD) later confirmed local reports that the blood-boosting drug EPO had been found in the physio’s hotel room.
AEPSAD said it, in conjunction with the International Association of Athletics Federations (IAAF), had also drug-tested more than 20 athletes.
One of the hot favourites for gold at the Rio Olympics, the 25-year-old Dibaba is the current world indoor and outdoor record-holder for 1,500m, and the reigning world champion for outdoor 1,500m and indoor 3,000m.
Genzebe Dibaba is the sister of Tirunesh Dibaba, a three-time Olympic champion, and Ejegayehu Dibaba, an Olympic silver medallist, and the cousin of former Olympic champion Derartu Tulu.
The younger Dibaba was named the IAAF’s female athlete of the year for 2015 after a sensational season that saw her win a gold and a bronze at the world championships in Beijing and break one of athletics’ oldest records, the outdoor 1500m, in Monaco.
It is understood the police raid in Spain took place the day after the Dibaba sisters arrived at Aden’s training camp.
The IAAF’s involvement in the operation should spare them some blushes if Aden, who has coached several African runners to Olympic and world titles, and the Dibabas are found to have cheated but there will also be a few red faces at British Athletics.
Aden, who ran for Somalia in the 1980s, has been used in the past by the British federation as an “unofficial facilitator” for training camps in Ethiopia, including at least one attended by double Olympic champion Mo Farah last year.
A spokesman for British Athletics said Aden had not been used in any role this year, as a result of changes it made following the controversy surrounding Farah’s American coach Alberto Salazar.
“All Aden did last year, for a very short period of time, was to hold a stop watch and shout out times to athletes as they completed their track sessions,” the spokesman said.
“There was no coaching or anything technical involved.”
He added that some overlaps with other training groups will inevitably occur, particularly in this part of Ethiopia as there is only one track.
Farah’s agent Ricky Simms made a similar point, stressing that his management group had no relationship with Aden whatsoever.