text: Hillary Clinton looks set to come under renewed pressure to explain herself after a letter revealed she had been asked about her use of private email by a House committee two years ago - but refused to answer. Representative Darrell Issa asked then Secretary of State Clinton whether she, or any of her senior staff, had used a personal email account 'to conduct official business' in December 2012. But Issa, who wrote as chairman of the House committee on oversight and government reform, was ignored until more than a month after Clinton had stepped down in February 2013. And even then, the reply did not answer the question - instead going into detail over the State Department's email policy. Silence: Representative Darrell Issa (left) asked the State Department about the use of personal email for official business in December 2012, but didn't receive any answer until Clinton (right) had left the department . The leaked letter, obtained by the New York Times, casts a further shadow over Clinton just days into her bid to become the Democrat's 2016 presidential candidate. The former First Lady found herself at the centre of a storm in recent months after it was revealed she used her personal address during her time as Secretary of State. Even her Twitter profile picture was dragged into the row: it showed her on her Blackberry apparently sending emails while en route to Libya in September 2011. But there is no record of any emails on her official account that day - and she has since removed the picture from her account. Clinton has confirmed that she exclusively used her private account, calling it a matter of 'convenience', admitting to deleting thousands of emails. Clinton, however, has insisted every relevant email was now in the hands of the State Department. But critics say by using her personal email account, she has avoided scrutiny. The presidential hopeful handed over 55,000 emails sent from her personal email account between 2009 and 2013 - her time as Secretary of State - but it is not yet known what they contained. However, it has already been claimed that the documents have 'huge gaps'. Shadow: Clinton is likely to want to play down this latest revelation as she begins campaigning in Iowa . Campaigning: Clinton is hoping to win over voters with a more personal approach than in 2007 . Clinton is likely to want to play down these latest revelations, as she begins a campaign for nomination which is set to last until the end of June next year. A Clinton aide told the New York Times on Tuesday 'her usage was widely known to the over 100 department and U.S. government colleagues she emailed, as her address was visible on every email she sent'. Clinton is currently on a two day tour of Iowa, opening her 2016 campaign with visits to a family-owned produce company and speaking with small-business leaders outside Des Moines. The decision to focus on smaller, more personal interactions during the campaign is in stark contrast to 2007, when she spoke to huge crowds. The grandmother-of-one will spend a second day in Iowa campaigning today.
target: Letter to State Department in December 2012 asked about personal email .
  But there was no response until March 2013 - seven weeks after Clinton left .
  Reply did not answer query about personal email use for official business .
  Latest revelation casts further shadow as Clinton begins White House bid .