Image copyright AP Image caption Hillary Clinton used a personal email address whilst US Secretary of State

Hillary Clinton's emails have been subpoenaed by a US Congressional hearing investigating the attack on the US embassy in Benghazi.

The US state department is already examining her use of a personal email as a possible breach of federal law.

It was revealed on Wednesday that Mrs Clinton had her own internet server at her home in New York.

In response, Mrs Clinton asked the US state department to swiftly release her emails.

In a tweet, she wrote: "I want the public to see my email. I asked State to release them. They said they will review them for release as soon as possible."

Personal server

The Republican-led committee has demanded that Mrs Clinton turn over all emails relating to the 2012 attack in Libya.

The chairman of the Benghazi committee, Trey Gowdy, told reporters "I want the documents. Sooner rather than later."

Democrats on the committee have criticised the decision arguing it is a politically-motivated hunt by Republicans,

"Everything I've seen so far has led me to believe that this an effort to go after Hillary Clinton, period," said Elijah Cummings.

The matter has been complicated by Associated Press reports that an internet server was registered under the name of Eric Hoteham at Mrs Clinton's home in Chappaqua, New York.

The correspondence of federal officials is considered government records under federal law and Mrs Clinton has already had to hand over 55,000 pages of emails to the State Department.

From 2009 to 2013, Mrs Clinton did not have a government email address, the US State Department told The New York Times.

Government watchdogs and former officials from the National Archives and Records Administration told the New York Times that Mrs Clinton's exclusive use of private email was a serious breach.

Others cited concerns that a personal email account could be vulnerable to hackers.

On Tuesday, Nick Merrill, a spokesman for Mrs Clinton, declined to say why she used a personal account at the state department, but defended its use. Mrs Clinton had complied with the "letter and spirit of the rules", Mr Merrill said.