The House Benghazi Committee has missed a self-imposed deadline to issue a report "before summer," the latest setback for a probe that has gone on for more than two years.

The inquiry has drawn scorn from Democrats who say the primary goal of the Republican-led investigation is to undermine Hillary Clinton's presidential bid.

The panel's chairman, South Carolina Rep. Trey Gowdy, says "the committee is working overtime to complete the investigation" and will "issue a report as soon as possible."

Clinton, who was secretary of state at the time of the deadly 2012 attacks, is expected to be nominated for president at the Democratic National Convention in five weeks.

The Sept. 11, 2012 attacks in Libya killed four Americans, including U.S. ambassador Chris Stevens.