Jofi Joseph, 40, was fired from his post on the NSC nuclear non-proliferation team last week after a months-long investigation into hundreds of Twitter postings, including criticisms of former Secretary of State Hillary Clinton, top NSC officials and the wives of political candidates, Politico reported Tuesday.
"It has been a privilege to serve in this administration and I deeply regret violating the trust and confidence placed in me," Joseph told Politico in an email.
He posted his anti-administration tweets for about two years under the pseudonym @natsecwonk.
During their investigation, officials also told Joseph they suspected he was responsible for another anonymous Twitter account, @dchobbyist, which included tweets about sexual encounters and escort services, among other things.
Joseph didn't respond to Politico's request for comment about the second account.
Joseph, a member of the administration's team that opened up preliminary talks over Iran's nuclear program in Istanbul, Turkey, earlier this year, worked with NSC officials and the State Department on extremely sensitive issues while secretly tweet-bombing them with comments such as, "Has s----y staff. #ObamaInThreeWords."
After the investigation, lawyers from the White House counsel's office confronted Joseph and ordered him to leave, two sources told Politico.
Joseph was to have rotated out of White House duty to a senior job in the Pentagon, an administration official told Politico.
A White House spokesman confirmed to The Daily Beast, which broke the story of Joseph's firing, that he no longer works there but declined further comment.
The revelation that Joseph was @natsecwonk was shocking because he was a familiar face among foreign policy practitioners, as is his wife Carolyn Leddy, a well regarded staffer for Republicans on the Senate Foreign Relations Committee, The Daily Beast said.
Joseph deleted the @natsecwonk account earlier this week.