A doping ring has been targeted by police raids at the International Ski Federation (FIS) Nordic Skiing World Championships, currently underway in Seefeld in Austria.
Nine people - five athletes and four others - have been arrested as part of a targeted operation against a worldwide drugs network.
Two of the athletes are Austrian, while one is from Kazakhstan and two are from Estonia.
They have not yet been formally identified.
Raids also took place in Erfurt in Germany in a coordinated operation involving both Austrian and German officials.
Two people were arrested there, one of whom is a doctor with reported links to doping in cycling.
According to a statement from the Austrian Federal Police Office (FPO), one athlete was caught "in the act".
"He was picked up with a blood transfusion in his arm," the FPO's Dieter Csefan is quoted as saying.
In a statement published on their website, the FIS said five cross-country athletes have been arrested during a "surprise raid".
"FIS is working closely with the Austrian public authorities in view of today's events and will follow up the cases and take the necessary actions in accordance with the FIS and World Anti-Doping rules," they said.
"FIS will fulfill its mandate as the governing body to ensure that the integrity of the sport remains intact and to protect all clean athletes."
It follows a recent documentary published by ARD, in which Austrian skier Johannes Dürr, who was convicted of doping after the Sochi Olympics in 2014, confessed he had doped in Germany.
In the piece titled "Doping Top Secret: Confession, Inside the mind of a doper", Dürr revealed how he cheated, admitting to blood transfusions and taking EPO and growth hormones.
Dürr confessed to having his blood manipulated at hotels near Munich Airport and in other places across Germany including Oberhof and Irschenberg.
He did not name anyone who helped him dope, with the raids instigated at least in part as an attempt to find co-conspirators.
"To what extent German athletes are suspected, was not known," a report in the German newspaper Suddeutsche Zeitung (SZ) reads, while German coaches and athletes have reportedly criticised Dürr's statements, suggesting, SZ says, that he was merely "seeking attention".
The Austrian police confirmed at a press conference that 16 properties had been raided across Austria and Germany.
"The BK, Office for Combating Organised Crime, succeeded in smashing an international doping network in cooperation with the Zollfahndungsamt Munich, Branch Lindau," they said.
"In the morning hours of 27 February 2019, in a coordinated action in Seefeld and in Germany, a total of nine people were arrested and 16 house searches executed by orders of the Attorney General Munich and the STA Innsbruck."
They said it follows months of investigations into a "German based criminal organisation" formed around a doctor named as "Mark S".
"This Erfurt-based criminal group is strongly suspected of having been doping top athletes for years to increase their performance in domestic and international competitions, thereby gaining illegal revenues," the police statement continued.
"In the course of a coordinated intervention in the presence of the German public prosecutor and German investigators, two members of the criminal group and five top athletes were arrested in Seefeld on the basis of orders granted by the court, and house searches were carried out.
"The arrested athletes are two Austrian, one Kazakh and two Estonian top athletes.
"Among the detainees are also two police athletes from the national squad cross country/national team, who are currently undergoing basic police training.
"At the same time, the 40-year-old sports physician Dr. med. Mark S. and another 40-year-old German accomplice [were] arrested and house searches [were] carried out.
"The investigations are still ongoing."
In a statement sent to insidethegames, the President of the Austrian Ski Federation (OSV) Peter Schröcksnadel said he is "shocked" that the Championships has now been "overshadowed" by a doping scandal.
"At the same time, the ÖSV would like to thank the investigating authorities for uncovering this obviously international doping network, which has been operating for years, and hopes that the backers and masterminds will be held accountable," he said.
"Nothing is more vile than buying better results through illegal performance-enhancing methods.
"I am deeply annoyed that some athletes seem to have learned nothing from the past.
"In the ÖSV zero tolerance applies to doping."
He also stressed that there is "no indication", OSV officials have been implicated.
"Regardless of that, I will suggest to the Bureau to completely reorganise cross-country skiing in the ÖSV after this season," he said.
"The ÖSV guarantees to do everything in its power against doping.
"But we can not guarantee that every individual will comply with the strict regulations.
"The responsibility is borne by each individual athlete, the consequences also.
"It is clear, who doped is immediately excluded from the ÖSV.
"The legal consequences will attract the authorities."
The World Anti-Doping Agency (WADA) has released a statement saying they are aware of the raids and are in "close communication with law enforcement authorities".
"The raids were part of a wider police operation targeting criminals from a number of European countries, and WADA's Intelligence and Investigations Department has been providing information and other assistance to the authorities in the course of their operation," a spokesperson said.
"This latest cooperation with Austrian law enforcement follows a WADA investigation into activities of the International Biathlon Union (IBU), which last year resulted in the initiation of a criminal investigation by police in Austria and Norway.
"Given the operation is ongoing, WADA can make no further comment at this time."
Last year Austrian police also carried out raids on the IBU headquarters in Salzburg.
That action followed evidence that former IBU President Anders Besseberg and secretary general Nicole Resch had been involved in a cover-up surrounding the doping of Russian athletes.
The raid was sparked by tip-off by WADA, who were investigating information provided by whistleblowers, including ex-Moscow Laboratory director Grigory Rodchenkov.
Austrian prosecutors revealed in a statement that the alleged wrongdoing covered a period from 2012 until the 2017 World Championships in the Austrian resort of Hochfilzen.
Besseberg and Resch were also accused of accepting bribes amounting to $300,000 (£211,000/€243,000) and other benefits in return for a favourable stance towards Russia - though they both deny wrongdoing.
Austrian police also raided the Kazakh team hotel at the World Championships in Hochfilzen.