The Swiss Federal Office of Justice has received a formal request from the United States to extradite seven FIFA officials arrested in Zurich in May.

The requests were received on Wednesday, within the deadline required by a bilateral treaty.

The process is, however, likely to be a lengthy one as the seven can challenge any extradition ruling, and can appeal to two higher courts. All seven men detained in Zurich, including three current and former members of FIFA's executive committee, already have objected to extradition. They face around 20 years in prison if convicted of the charges.

The extradition requests are based on a U.S. probe into alleged bribery worth more than $100 million involving high-ranking officials at football's world governing body.

Six of the seven, including FIFA vice president and former CONCACAF president Jeffrey Webb, were arrested during a dawn raid on a Zurich hotel days before FIFA's Congress, plunging the world governing body into crisis.

A statement from the Federal Office of Justice said: "The USA has asked Switzerland to extradite the seven FIFA officials arrested in Zurich. The formal extradition requests were submitted to the Federal Office of Justice (FOJ) yesterday evening.

"The seven FIFA officials were arrested in Zurich on May 27, 2015, on the basis of a request from the USA, and detained pending extradition," it said.

"On July 1, 2015, the US embassy in Bern submitted the formal extradition requests within the deadline laid down in the bilateral extradition treaty.

"The requests are based on the arrest warrants issued on May 20, 2015, by the United States Attorney's Office for the Eastern District of New York, which is investigating the high-ranking FIFA officers on suspicion of taking bribes worth over $100 million."

The seven will be heard by Zurich police and granted a 14-day period to respond to federal officials about the extradition request, the Swiss justice ministry said.

Swiss justice officials will then rule "within a few weeks" on whether to extradite them. That ruling can be appealed to Switzerland's top criminal court and supreme court.

On Wednesday, Sepp Blatter challenged his critics to prove that he is corrupt, and insisted that anybody who accuses him of guilt by association to the corruption scandal engulfing world football's governing body "should go to jail."

Blatter announced on June 2 he would step down as FIFA president at an extraordinary congress to be held between December and March.

The Swiss is himself reportedly under investigation by the FBI and will not attend the Women's World Cup final in Canada this week because of the twin investigations by American and Swiss justice authorities.

In addition to the Cayman Islands' Webb, the seven officials arrested include Eugenio Figueredo of Uruguay, who was arrested two days before his FIFA vice presidential term expired.

The group also includes Costa Rican football federation president Eduardo Li, who was arrested two days before he was due to formally join FIFA's executive committee, as well as former Brazilian federation chief Jose Maria Marin, who led the 2014 World Cup local organizing committee and is a member of the FIFA panel organizing the men's and women's tournaments at next year's Olympic Games.

The others are Venezuela FA chief Rafael Esquivel; FIFA staffer Julio Rocha, a development officer from Nicaragua; and Costas Takkas, a Briton who works for CONCACAF president Webb.

The other seven men among the 14 indicted include disgraced former FIFA vice president Jack Warner of Trinidad and Tobago, and former FIFA executive committee member Nicolas Leoz of Paraguay, the longtime former president of South American governing body CONMEBOL.

A further four men have entered guilty pleas which were unsealed in May. They include American former FIFA executive panel member Chuck Blazer and two sons of Warner. The indictment revealed that Blazer admitted being part of a $10 million bribe scheme with Warner for supporting South Africa's successful bid to host the 2010 World Cup.

A third South American FIFA voter was also involved, Blazer alleged.

FIFA has acknowledged that its secretary general, Jerome Valcke, helped transfer the money through its accounts at South Africa's request. FIFA and Valcke said the cash was believed to be for football projects for the African diaspora in the Caribbean, and was approved by Julio Grondona of Argentina, the chairman of FIFA's finance committee who died last year.

American law enforcement officials have confirmed that Blatter is a target of the investigation, which is expected to bring more indictments due to pressure built from an American case and a separate Swiss federal investigation of money laundering linked to the 2018 and 2022 World Cup hosting awards to Russia and Qatar, respectively.

Blatter cannot be extradited from his native Switzerland to the U.S. without his consent. Still, he risks arrest in many countries.