Former US Secretary of State Hillary Clinton speaks during the unveiling of "No Ceilings" and the "Not There Yet: A Data Driven Analysis of Gender Equality study" in New York March 9, 2015. [Photo/Agencies]

WASHINGTON -- Questions are mounting over 2016 US presidential contender Hillary Clinton's private email account as the Democratic front-runner remains silent on the controversial issue.

Last week it was discovered that Clinton had solely used a private email account and kept private servers in her home to conduct business during her four-year stint as head of the State Department, instead of a government-issued email account, which is the norm.

Critics are blasting Clinton over the highly unusual practice, arguing that she could have compromised US national security and that she may also have violated US laws governing transparency among public officials.

The move has also sparked myriad questions over whether there was any intent to keep information away from the public.

Clinton has ordered the State Department to hand over 55,000 pages of emails, but critics say Clinton will still be able to decide which emails the public can see, and the State Department says it does not know for sure whether there were any deleted emails.

At the same time, Senator Dianne Feinstein said Sunday on NBC's "Meet the Press" that Clinton needs to "come out and state exactly what the situation is," explaining that her continued silence on the issue could hurt her.

The senior senator is the first Democrat to call on Clinton to address the issue in public.

"Democrats want to make sure that Hillary Clinton gets out front on the email issue and answer basic questions. They do not want that controversy to torpedo her campaign before it gets off the ground," Brookings Institution's senior fellow Darrell West told Xinhua.

"She needs to explain why she relied on a private account," West said.