President Barack Obama said Monday those responsible for any improper scrutiny of conservative groups' tax status would be held "fully accountable," hours before it emerged that the current and former heads of the Internal Revenue Service were informed last May that tea-party groups had been targeted.

The IRS said in a statement that acting Commissioner Steven Miller was first told by the agency staff on May 3, 2012, that some specific groups' applications for tax-exempt status were improperly selected for extra...