CHICAGO -- Federal prosecutors on Wednesday asked for another three months to indict Illinois Gov. Rod Blagojevich, saying they must review "thousands" of recently intercepted phone calls and talk with multiple people who have come forward to discuss the corruption investigation.

A 30-day deadline to return an indictment against Blagojevich was set to expire Jan. 7.

Blagojevich, a second-term Democrat, has denied any wrongdoing and he has retained a high-profile criminal defense attorney. On Tuesday he selected former Illinois attorney general Roland Burris to replace Obama in the Senate.

In Wednesday's motion, prosecutors asked for more time to review "thousands of phone calls... intercepted between late-October 2008 and early-December 2008." They also said the five-year investigation was "complex" and, while noting that some arguments for an extension could not be disclosed publicly, pointed to the need to talk to more people.

"Multiple witnesses have come forward in recent weeks to discuss their knowledge of criminal activity in relation to the ongoing investigation," according to the motion.

The document also hints at the possibility that more individuals could be charged.

"The government has been conducting a diligent and thorough investigation in this case, but the investigation includes multiple defendants and potential defendants," according to the document.

U.S. Attorney spokesman Randall Samborn declined to give further details.

According to the motion, attorneys for Blagojevich and his former chief of staff, John Harris, who was also arrested, have not objected to the extension. Blagojevich attorney Ed Genson declined to comment Wednesday.

A federal judge is scheduled to review the motion at a court hearing Monday.

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Associated Press writer Deanna Bellandi contributed to this report.