From CNN Justice Producer Terry Frieden

WASHINGTON (CNN) -- Attorney General Alberto Gonzales plans to formally notify House Speaker Dennis Hastert as early as today the FBI has opened an initial inquiry into possible criminal violations by resigned Congressman Mark Foley, Justice Department sources said Monday.

The letter from Gonzales is a response to the House Speaker's letter Sunday urging not only a probe of Foley, but a broad investigation which would examine "Members of Congress, employees of the House of Representatives, or anyone outside the Congress" who had knowledge of the e-mails Foley sent to House pages.

Hastert called for the Justice Department to "undertake an investigation into who had specific knowledge of the content of any sexually explicit communications between Mr. Foley and any former or current House pages and what actions such individuals took, if any, to provide them to law enforcement."

One Justice Department official, who asked not to be identified, termed that request "highly unusual," but said if the FBI assessment of Foley leads to a full-blown criminal investigation that indications of any possible violation of federal laws will be aggressively pursued.