The FBI on Wednesday confirmed that its investigation into corruption scandal at world football's governing body includes scrutiny of the awarding of the World Cup to Russia in 2018 and Qatar in 2022, a law enforcement official told Reuters.

The review of awards to host both World Cups would be part of a probe that goes beyond the initial allegations in an indictment announced a week ago of FIFA officials, an unnamed source told Reuters.

However, a source close to the Qatar 2022 World Cup told the BBC's Richard Conway that "American law enforcement officials have not been in contact and there have been no requests for information."

Switzerland has launched an investigation into the bidding process for the 2018 and 2022 World Cups.

The FBI is examining the stewardship of FIFA by its longtime president Sepp Blatter, who on Tuesday unexpectedly announced plans to resign, Reuters reported.

Blatter was just re-elected to a fifth term as president at the FIFA Congress on Friday, two days after a crisis erupted and seven officials were arrested in Zurich as part of the United States Justice Department corruption investigation.

Blatter was not among the 14 officials indicted but ABC News reported on Tuesday he was a target of the probe.

The seven arrested officials, including two FIFA vice presidents, one member-elect of the FIFA executive committee and one FIFA staffer, all face extradition to the United States in a process which could last months.

Once in the U.S. they will be questioned about involvement in alleged racketeering, money-laundering and wire fraud in a $150 million bribe scheme spanning more than two decades.

The seven in Zurich have until next Monday to appeal being detained by Swiss authorities.

Their best chance of being released on bail lies with their lawyers either finding flaws in how American and Swiss agencies processed and handled the arrests, or a lenient judge.

"Release on bail is possible, but it's very, very rare,'' said Folco Galli, spokesman for the Swiss Federal Office of Justice in Bern.

The next deadline in the Swiss extradition process is July 3. The U.S. must submit its formal extradition request by then and may be in no hurry to do so.

All seven detainees could be feeling a long way from their home countries in South and Central America and residences in the U.S.

"We will publish a press release as soon as these requests have been submitted," Galli said on Wednesday.

The Swiss justice office will examine the merits of each request and likely issue an extradition order within a month or two.

One condition is that the allegations each faces in the U.S. would also be punishable in Switzerland.

The Swiss authorities will not have an opinion on the likely guilt or innocence of each detainee. That is for the American courts to decide, Galli said.

An order granted can be appealed to the Swiss Criminal Court in Bellinzona, in the Italian-border canton (state) of Ticino. A further appeal route goes to the Swiss Federal Tribunal in Lausanne.

That whole process could last at least six months, depending on how much resistance is put up by the seven.

The outgoing FIFA president will not be detained in his home country on behalf of American prosecutors.

As a Swiss national, Blatter cannot be extradited by Switzerland. Still, the 79-year-old Blatter becomes more exposed if traveling abroad where a warrant for his arrest and extradition could be sought by the U.S.

FIFA tournaments are being played this month in New Zealand and Canada. Under normal circumstances, FIFA protocol would require Blatter to attend the Under-20 World Cup final in Auckland on June 20 and the Women's World Cup final on July 5 in Vancouver.

FIFA said on Wednesday that Blatter does not have any confirmed travel plans in the next two weeks.

Information from The Associated Press was used in this report.