Hillary Clinton used a personal email account during her time as US secretary of state, rather than a government-issued email address, potentially hampering efforts to archive official government documents required by law.

Mrs Clinton's office said nothing was illegal or improper about her use of the non-government account and that she believed her business emails to the US state department and other .gov accounts would be archived in accordance with government rules.

The revelations come as the former first lady is gearing up for a possible presidential campaign in 2016. Although she has not yet announced her candidacy, she is the clear early favourite for the Democratic nomination.

"Like secretaries of state before her, she used her own email account when engaging with any department officials," Clinton spokesman Nick Merrill said. "For government business, she emailed them on their department accounts, with every expectation they would be retained. When the department asked former secretaries last year for help ensuring their emails were in fact retained, we immediately said 'yes'."

"Both the letter and spirit of the rules permitted state department officials to use non-government email, as long as appropriate records were preserved," he said.

Deputy state department spokeswoman Marie Harf said the agency asked former secretaries of state Madeleine Albright, Colin Powell, Condoleezza Rice and Mrs Clinton last year for records that should be preserved.

In response to that request, Mrs Clinton provided emails from the personal account that she used during her time as the nation's top diplomat in President Barack Obama's first term from 2009 to 2013.

However, she also said that the department has "long had access to a wide array" of Mrs Clinton's records, including emails sent between her and officials with an official state.gov email address.

Ms Harf said Mrs Clinton's successor, John Kerry, is the first secretary of state to primarily use an official state.gov email account and that the department is now updating its records preservation policies to bring them in line with current regulations. That includes regularly archiving all of Mr Kerry's emails.

Among the messages Mrs Clinton provided were 300 that met the criteria for a request for relevant emails from the House Select Committee investigating the September 2012 attack on the US diplomat mission in Benghazi, Libya, Ms Harf said. Those emails have been turned over to the committee, she added.

Mrs Clinton's use of a personal email account while secretary of state was first reported by The New York Times.