A White House national security official has been fired after he was revealed to be the man behind an anonymous Twitter account critical of the Obama administration.

A senior administration official confirmed to Fox News that Jofi Joseph, a director in the nuclear non-proliferation section of the White House's national security section, was fired last week after he was discovered as being the man behind the "@netsecwonk" Twitter account. Joseph's firing was first reported by The Daily Beast.

Joseph admitted he was responsible for the account in an email to Politico Monday evening, writing, "What started out as an intended parody account of DC culture developed over time into a series of inappropriate and mean-spirited comments. I bear complete responsibility for this affair and I sincerely apologize to everyone I insulted."

The account had been active since February 2011 and had been used to criticize the administration's policies and occasionally the personal qualities of its top officials.

For example, according to Tweets saved by the Daily Beast before the "@natsecwonk" account was shutdown last week, White House senior adviser Valerie Jarrett was referred to as a "vacuous cipher."

Within the last month, Joseph stated that former Secretary of State Hillary Clinton had "few policy goals and no wins" in the Middle East in a tweet quoted by Reuters. He also appeared to support an investigation into the 2012 terror attack on the U.S. consulate in Benghazi, Libya, tweeting, "Look, [Rep. Darrell] Issa is an ass, but he's on to something here with the @HillaryClinton whitewash of accountability for Benghazi."

But Joseph turned his anonymous fire on Republicans too, once asking "[W]hen will someone do us the favor of getting rid of Sarah Palin and the rest of her white trash family?" in a tweet last October. John Noonan, a national security staffer on Mitt Romney's 2012 presidential campaign, was referred to as an "overweight paid Romney shill."

Prior to working at the White House, Joseph served as principal adviser on foreign policy, national security, and homeland defense issues to Sen. Robert Casey, D-Pa. Between 2001 and 2004, he had served as a staffer on the Senate Foreign Relations Committee and advised current Vice President Joe Biden, then a Senator from Delaware and the committee's chairman about arms control, non-proliferation and U.S. military assistance.

Fox News' Ed Henry contributed to this report.