FBI interview Hillary Clinton about her use of a private email server while she was Secretary of State

It is reported that the Presidential hopeful was grilled for hours on the subject

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Image: Tony Dejak / AP/Press Association Images

The FBI has interviewed Hillary Clinton about her use of a private email server while she was Secretary of State.

The Democratic White House hopeful's campaign said the "voluntary" meeting with federal agents took place on Saturday.

The interview took place at the FBI headquarters in Washington DC and lasted three and a half hours.

"She is pleased to have had the opportunity to assist the Department of Justice in bringing this review to a conclusion," said her spokesman, Nick Merrill.  "Out of respect for the investigative process, she will not comment further on her interview."

It is not known whether she had a lawyer present.

The interview does not mean she will face criminal prosecution, a scenario most legal experts deem highly improbable.

But it is not ideal for Democrats to have their standard bearer grilled by the FBI weeks before she formally accepts the party's presidential nomination.

Mrs Clinton, who aims to become the nation's first female commander-in-chief in November's election, has apologised for using a private account exclusively from her upstate New York home during her four years as America's top diplomat.

She handed over 30,000 of the emails to the State Department, but deleted another 30,000 which she said were "personal".

The scandal has dogged her campaign for more than a year and fanned voter concerns she is not trustworthy.

Critics say her private email breached rules about protecting classified documents from cyber attack and may have amounted to a crime.

The FBI interview came amid revelations that America's top prosecutor, US Attorney General Loretta Lynch, held an impromptu meeting with Mrs Clinton's husband, former president Bill Clinton, at the airport in Phoenix, Arizona, this week.

News of the exchange triggered a political firestorm, and Ms Lynch vowed on Friday to "accept" the recommendations of the FBI and the prosecutors on whether to charge Mrs Clinton.

She admitted the private encounter with Bill Clinton had "cast a shadow" over the investigation into the emails.

Ms Lynch said Mr Clinton had talked about his grandchildren and said he had been playing golf in Arizona. 

Republican presidential candidate Donald Trump tweeted: "Does anybody really believe that meeting was just a coincidence?"