The suspects include soccer players currently playing in the first division, others who had played in the top flight but are now retired, active players in the second division and "presidents and executives" of clubs, police said.
The investigation remained under secrecy so no names or details about the affected matches were released by authorities. Spanish news agency Europa Press said two of the players arrested play for first-division teams, though none of the country's top clubs were apparently involved.
The investigation was being handled by a court in Huesca, a small city in northeastern Spain. Images showed police conducting an operation at the headquarters of the club by the same name, which was relegated this season after playing in the top-flight for the first time.
Huesca released a statement denying any wrongdoing and saying the judicial probe that was opened by authorities was not directly related to the club. The statement came after Spanish media said a club official was among those arrested by police.
Valladolid, also named in Spanish media reports for allegedly having one of its players arrested, also released a statement denying wrongdoing. It called for a thorough investigation of those involved.
Speaking in a news conference, National Police general director Francisco Pardo didn't confirm reports that the first-division match between Valencia and Valladolid was among those investigated for match-fixing. Valencia won the match 2-0 to secure the final Champions League spot in the Spanish league.
The police said their investigation, named "Oikos," has led them to identify "at least three" matches in the first, second and a lower division that they believe were fixed. The suspected fix for the second-division match involved a massive increase in the amount of bets placed on the result that was 14 times greater than the average, according to police.
"These operations require a lot of work. They take place over a long period of time and require a lot of cooperation," Pardo said. The Spanish league said the arrests were the result of an investigation it instigated. The league said it contacted authorities about possible match-fixing involving a second-division match in May 2018, but it did not provide details about the teams or players involved.
Additionally, the league said during the 2018-19 season it informed police of eight suspected cases of "acts related to match-fixing in lower, non-professional divisions and international friendlies."
The league said it also "sent alerts" about 18 matches in which players possibly placed bets on the outcomes of games in lower and non-professional divisions. The league thanked the National Police for the "extraordinary work done to dismantle what appears to be an organized criminal group dedicated to obtaining economic benefits through the predetermination of soccer matches."
"This police operation demonstrates the effectiveness of integrity protection systems implemented by LaLiga to protect the cleanliness of all competitions in Spanish soccer," the league said.
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