The FBI and U.S. prosecutors were investigating Sepp Blatter, the FIFA president who announced his resignation on Tuesday, as part of the probe that led to last week's stunning indictments, sources familiar with the case told ABC News.

The FBI declined to comment because Blatter has not been publicly identified as a target of the investigation.

U.S. authorities last week indicted 14 people -- nine football officials and five sports-marketing executives -- who face charges of wire fraud, racketeering and money laundering. They are accused of accepting more than $150 million in bribes.

ABC News reported that the investigation hoped to use those indicted to provide information that could lead to charges against their superiors -- much as federal agents would in a mob racketeering case.