Hillary Clinton interviewed by FBI about private emails while Secretary of State

Presumptive Democratic nominee Hillary Clinton was questioned by the FBI in a long-awaited interview Saturday over the use of her private email server, an aide said.

The interview's purpose was to delve into whether Clinton mishandled classified information submitted on her private email system while she served as secretary of state. Her top staffers have already given testimony.

The interview happened at the FBI headquarters in Washington, D.C., and lasted approximately three and a half hours, sources said.

"Secretary Clinton gave a voluntary interview this morning about her email arrangements while she was Secretary. She is pleased to have had the opportunity to assist the Department of Justice in bringing this review to a conclusion. Out of respect for the investigative process, she will not comment further on her interview," Nick Merrill, a Clinton spokesman, said in a statement.

Clinton has no public events scheduled for the July 4th weekend.

See photos of Hillary Clinton throughout her career:

Rumors that the FBI interview was to take place Saturday, first reported by The Daily Caller, emerged as the Clinton campaign was mired in controversy over a meeting between Attorney General Loretta Lynch and former President Bill Clinton. The two met on Lynch's airplane on a tarmac in Phoenix on Monday.

The attorney general insisted their talk was purely "social" and said they didn't talk about the emails that the Justice Department are currently reviewing. But she expressed regret Friday for the meeting.

"I certainly wouldn't do it again because I think it has cast a shadow over how this case will be perceived," Lynch said.

Related: Lynch Won't Recuse Herself From Clinton Case

Meanwhile, presumptive GOP nominee Donald Trump was spending the weekend vetting potential running mates, including former House Speaker Newt Gingrich, New Jersey Gov. Chris Christie, and Indiana Gov. Mike Pence.

Trump was incredulous over Bill Clinton's meeting with Lynch, saying in a speech Friday, "He opened up a Pandora's box."