The FBI has confirmed it is investigating Clinton's use of her own server

Among those believed to have received the emails was Huma Abedin

Hillary Clinton shared intelligence files labelled Top Secret with her aides using her own personal email server, it has been claimed.

The information, which was contained on the former secretary of state's personal email server, was deemed far too sensitive to release according to reports.

It is alleged that several of Clinton's staff, including Cheryl Mills, Huma Abedin, Jake Sullivan and Philippe Reines had access to the information.

It is believed that more than a dozen email accounts received the sensitive data.

Scroll down for video

Former Secretary of State Hillary Clinton, pictured here shortly before her loss in the New Hampshire primary shared 'Top Secret' files with her aides using her own personal unsecured email server, it was claimed

Clinton's aide Huma Abedin, right, is believed to be among those who received the 'Top Secret' files

There is no evidence to show that these individuals, as well as Patrick F. Kennedy, Under Secretary for Management at the State Department, had the appropriate high-level security clearance to access the files, according to Fox News.

A source told the network that top secret intelligence was 'broadly shared' across the unsecured email system.

Security expert Dan Maguire told Fox: 'My contacts with former colleagues and current active duty personnel involved in sensitive programs reveal a universal feeling that the HRC [Hillary Rodham Clinton] issue is more serious than the general public realizes. Most opine they would already be behind bars if they had apparently compromised sensitive information as reported.

'The intelligence community is undoubtedly conducting damage assessments and evaluating the viability of any ongoing operation that may have been exposed to unauthorized personnel. The vulnerability of HRC’s server to foreign government hacking cannot be overlooked - even the DCI, John Brennan, has been the target of hackers.'

Meanwhile, the FBI has formally confirmed it is investigating Hillary Clinton's private emails, giving fuel to a controversy that the frontrunner for the Democratic presidential nomination has been unable to put behind her.

Republican opponents claimed Clinton, pictured, should withdraw from the presidential race over the scandal

FBI General Counsel James Baker said the FBI's investigation into Clinton's use of a private email server while she was secretary of state is 'ongoing'.

Clinton has repeatedly denied doing anything wrong.

Although the FBI's investigation first became public in July, the Republican Party jumped on the latest news, saying it should disqualify her from the presidency.

Republican National Committee chairman Reince Priebus said: 'The investigation into Hillary Clinton's secret email server is far from the routine 'security review. Clinton's conduct was a severe error in judgment that grossly endangered our national security and put highly classified information at risk.'

Clinton acknowledged in March that she exclusively used a private email account and private server from 2009 to 2013 while secretary of state, opting against a government account despite official recommendations.

Although the FBI letter -- filed by the Justice Department in federal court in connection with a Freedom of Information Act lawsuit -- provides no details about the investigation's scope or content, it suggests one of the favored Republican lines of criticism against Clinton's campaign is far from exhausted.