Two key Internal Revenue Service (IRS) employees implicated in the harassment of conservative groups have received threats, according to a Reuters report.

Former Acting IRS Commissioner Steven Miller, who was fired by President Obama last month, has been physically threatened, an anonymous source told the news agency.

The former head of the tax-exempt division, Lois Lerner, has also received threatening calls and emails.

Lerner was placed on administrative leave by Danny Werfel, the new action IRS commissioner.

Last month, the Treasury Inspector General for Tax Administration (TIGTA) concluded that the IRS has improperly handled the requests of scores of Tea Party groups to become tax-exempt social welfare organization. The harassment was not extended to liberal organizations seeking the apolitical tax-free status, TIGTA said.

The IRS revelations have provoked a vigorous House Oversight Committee investigation and many Republicans view it as a political boon for the party heading into the 2014 election season.