Hillary Clinton's nascent presidential campaign is facing its first crisis after it emerged that the former secretary of state may have broken the law by using a private email account for official government business.
Mrs Clinton never set up a State Department government email address during her four years as America's top diplomat. She used a personal account where her messages would not be archived automatically.
US law requires that senior officials save their emails and Republicans said that the personal account "raises serious questions" about whether Mrs Clinton was trying to hide her communications.
Jeb Bush, her potential Republican rival in the 2016 election, challenged Mrs Clinton to release her emails in the name of transparency. Even some Democrats expressed disquiet over her use of a private account, which was first reported by the 'New York Times'.
Robert Gibbs, Barack Obama's former White House press secretary, said the scenario was "highly unusual".
Mrs Clinton was an ardent Blackberry user during her four years as secretary of state.
It was not clear if her personal "clintonemail.com" address was encrypted and if it may have been vulnerable to hacking by foreign governments seeking to steal American secrets.
All senior officials must preserve their emails so they can be handed over to government watchdogs, historians or anyone who requests them under freedom of information laws.
Mrs Clinton may have stayed within the law if she submitted all government business emails sent from her personal account to the official US archives.
A spokesman for Mrs Clinton said she had complied with "letter and spirit of the rules" because all her messages to US government officials would have been saved on their accounts.
The spokesman did not address whether she used her personal account to email foreign leaders or non-US officials. (© Daily Telegraph, London)