SPRINGFIELD — Federal prosecutors Thursday refused to say when directly asked whether Dr. Eric E. Whitaker, a close friend of President Barack Obama, is a target in an ongoing grant-fraud case that resulted in the indictment of Whitaker’s onetime top state aide.

But Whitaker later in the day released a short statement that said he is cooperating in the federal investigation of Quinshaunta R. Golden, who was his chief of staff when he headed the Illinois Department of Public Health between 2003 and 2007.

Golden, 44, of Homewood, was accused Wednesday of pocketing about $433,000 in kickbacks on state health department contracts and grants she oversaw.

“I had no firsthand knowledge of the activities outlined in this indictment and was not involved in any way,” Whitaker said in the statement. “As requested by the U.S. attorney, I have been fully cooperating with the investigation into these matters.”

In taking questions about the indictment at a news conference, U.S. Attorney James Lewis dodged a question about whether Whitaker is a target of the probe.

“I honestly do appreciate the question,” Lewis told reporters. “I honestly had the feeling you might ask, and I accept that you’re responsible when you ask. But I’m responsible for what I answer, and my answer is there is nothing in the material you have today that leads towards an answer to that question.”

Lewis also would not say whether Whitaker has been interviewed by investigators or is otherwise cooperating. But the top federal prosecutor in the Central District of Illinois stressed decisions on proceeding with Golden’s indictment were made “locally,” not by Attorney General Eric Holder or his aides, and that the grant-fraud investigation would not reach Obama.

Lewis answered vaguely when asked if there is any evidence that Whitaker knew about Golden’s alleged wrongdoing. “There’s nothing in this material you’re being provided with today that indicates that,” he said. Pressed on whether that answer meant Whitaker did not know about it, Lewis grinned and said, “I think I just answered that.”

Whitaker became health chief under former Gov. Rod Blagojevich on Obama’s recommendation. The Sun-Times first reported in 2010 that email and other state records belonging to him had been subpoenaed by a grand jury.

Whitaker remains very much in the president’s inner circle. On Saturday, he played a round of golf with Obama and 10 other friends of the president at a golf course outside Washington, D.C. The group celebrated Obama’s 52nd birthday the next day.