The parents of two Americans killed in the 2012 attack on a United States diplomatic mission in Benghazi, Libya, filed a lawsuit on Monday against Hillary Clinton, saying that her “‘extreme carelessness’ in handling confidential and classified information” while secretary of state contributed to the conditions that led to their sons’ deaths.

In the wrongful-death lawsuit, Patricia Smith and Charles Woods charge that the attack that killed four Americans, including their sons, Sean Smith and Tyrone Woods, “was directly and proximately caused, at a minimum” by Mrs. Clinton’s use of a private email server while in the State Department.

The suit — which was brought by the conservative lawyer and longtime Clinton nemesis Larry Klayman on behalf of the families — also accuses Mrs. Clinton of having made “false and defamatory statements negligently, recklessly and purposefully and/or intentionally with malice” in her public comments, including those about the connection between the attack and an anti-Muslim YouTube video.

Both Ms. Smith and Mr. Woods have spoken out publicly against Mrs. Clinton during the election campaign.