Attorney General Eric H. Holder Jr. said on Tuesday that he had ordered the Justice Department and the F.B.I. to open an investigation into whether Internal Revenue Service officials broke any criminal laws by singling out conservative groups for special scrutiny.
The activities of I.R.S. officials are already the subject of an investigation by the agency's inspector general. The results of that inquiry, which are expected in the next several days, are likely to detail how officials at the agency selected political groups for extra scrutiny about their tax status.
Speaking at a news conference called on Tuesday to discuss Medicare fraud, Mr. Holder said that he had ordered a second investigation to determine whether any criminal laws may have been broken by the officials at the tax collection agency.