WASHINGTON — A federal watchdog investigating whether the Internal Revenue Service unfairly targeted conservative political groups seeking tax-exempt status said that the agency also scrutinized organizations associated with liberal causes from 2004 to 2013.

The findings by the Treasury Department’s inspector general mark the end of a political firestorm that embroiled the I.R.S. in controversy, led to the ouster of its commissioner and prompted accusations the tax collection agency was being used as a political weapon by the Obama administration.

The exhaustive report, which examined nine years worth of applications for tax-exempt status, comes after a similar audit in 2013 found that groups with conservative names like “Tea Party,” “patriot” or “9/12” were unfairly targeted for further review.

The new report found that the I.R.S. was also inappropriately targeting progressive-leaning groups. While the investigation does not specify the political affiliations of the groups, names that were flagged included the words “Progressive,” “Occupy,” “Green Energy,” and Acorn — the acronym for the now defunct Association of Community Organizations for Reform Now.