WASHINGTON -- Hillary Rodham Clinton ran her own personal computer system for handling emails while serving as secretary of state, according to Internet records reviewed by The Associated Press. The practice offered a measure of privacy to one of the world's most scrutinized women, but could subject her to more criticism ahead of a likely presidential campaign.

Clinton's email practices attracted attention this week when The New York Times reported that she had exclusively used a personal email account for State Department business. A Clinton spokesman said that wasn't improper, and that emails would be archived in accordance with government rules.

Republicans are signalling that questions about Clinton's use of a private email account while she was secretary of state will follow her into her widely anticipated presidential campaign.

Republican leaders, who control the investigative powers of Congress, say the revelations reaffirm their long-held portrayal of Bill and Hillary Clinton as secretive and playing by their own rules.

Democrats dismiss the accusations as trivial and question whether the emails will resonate with voters in an election 20 months away.

But as the presidential nominating season begins, Clinton's use of a personal email account for State Department business has stoked questions about transparency that threaten to cloud her early steps as the Democratic Party's overwhelming favourite White House prospect.

In particular, they question whether she has been forthcoming with a Republican-led congressional investigation into the attack on the U.S. diplomatic compound in Benghazi, Libya, in 2012, when Clinton headed the State Department. The department says Clinton has turned over 300 emails to the committee conducting the investigation.

The Republican-led House Select Committee on Benghazi issued subpoenas Wednesday to demand additional material from Clinton

The committee said it also has issued a subpoena to the State Department for all other individuals who have relevant information.

Clinton has not described her motivation for using a private email account -- hdr22(at)clintonemail.com, which traced back to her own private email server registered under an apparent pseudonym -- for official State Department business.

A number of federal and state officials have used private email accounts for official business. But generally they rely on conventional email providers, such as those offered by Microsoft and Google.

What is extraordinary in Clinton's case is the use of a server traced back to an Internet service registered to the home she shares with former President Bill Clinton outside New York City.

That would give her more control over limiting access to her message archives. It could help her fend off government or private subpoenas in criminal, administrative or civil cases.

A spokesman for Clinton did not respond to requests seeking comment from the AP on Tuesday. Clinton ignored the issue during a speech Tuesday night.

Clinton's official emails would be accessible to anyone who requested copies under the Freedom of Information Act. Under the law, anyone can compel the government to turn over copies of federal records for zero or little cost. Since Clinton effectively retained control over emails in her private account even after she resigned in 2013, the government would have to negotiate with Clinton to turn over messages it can't already retrieve from the inboxes of federal employees she emailed.

The AP has waited more than a year under the open records law for the State Department to turn over some emails covering Clinton's tenure as America's top diplomat, although the agency has never suggested that it didn't possess all her emails.

Clinton's private email account surfaced publicly in March 2013 after a convicted Romanian hacker known as Guccifer published emails stolen from former White House adviser Sidney Blumenthal. The Internet domain was registered around the time of her secretary of state nomination.