Hillary Clinton
Hillary Clinton Reuters

A federal judge in Washington on Wednesday ordered that Democratic presidential candidate Hillary Clinton may have to testify in a lawsuit related to the private email server she used while serving as Secretary of State, Reuters reports.

U.S. District Judge Emmet Sullivan said the parties in the case, the State Department and conservative watchdog group Judicial Watch, also struck an agreement about the scope of the testimonies that some of Clinton's former top aides will give in the case.

Those testimonies, known as discovery, will take place over the next eight weeks and may yield information that would require Clinton herself to be deposed, Sullivan said in an order quoted by Reuters.

Clinton's use of a private server in her New York home for her government work is being investigated by the Federal Bureau of Investigation, the State Department's internal watchdog and several Republican-controlled congressional committees.

Clinton has said she used private emails out of "convenience", though she has also admitted it "would have been better" to have two accounts to separate work and personal emails.

She has apologized for the use of a private email server, even though she had insisted she didn’t need to apologize because "what I did was allowed."

Critics, including likely Republican presidential election rival Donald Trump, say Clinton endangered government secrets and evaded transparency laws but she denies any wrongdoing.

While Clinton has denied that she sent or received classified emails from her private server, it was revealed recently that some of her mails were beyond "top secret".

Judicial Watch brought a lawsuit against the State Department to gain access to records related to a Clinton aide's employment. The Federal Bureau of Investigation is also probing her email arrangement, noted Reuters.

"This is a very great victory for transparency and, despite the best efforts of the Obama administration and the Clinton camp, it looks like we might finally get some answers under oath about the Clintons' illicit email system," said Tom Fitton, president of Judicial Watch.