The FBI's probe of the mortgage lending industry grew Tuesday into an investigation of 17 firms, concerns large companies and could take years to conclude, FOX News has confirmed.

FBI officials told Reuters in an interview Tuesday that the investigation is likely to expand, but declined to be more specific. Corporate employees ranging from senior executives to lower ranks are likely targets.

An FBI official declined to tell Reuters whether the collapse of mortgage giant Bear Stearns was a focus of probe.

FOX News' Ian McCaleb contributed to this report.