Washington (AFP) - Relatives of two men killed in the 2012 attack on a US consulate in Libya have filed a lawsuit blaming the deaths on Hillary Clinton's "reckless" handling of classified information in her private email server.

While secretary of state, Clinton conducted official government business on a private server at her home, which critics say exposed official US correspondence to possible hacking attacks from foreign governments and terror operatives.

The FBI concluded last month that the Democratic presidential nominee had been "extremely careless" with classified information on her server, but nevertheless declined to recommend criminal charges against her over the scandal.

US authorities ended their probe into the matter, but Clinton's political enemies have been trying to keep controversy over her email server alive, including linking it to the attack in Benghazi nearly four years ago.

Parents of two American security agents at the consulate in their wrongful death suit file Monday against Clinton allege that terrorists were able to determine the men's whereabouts because of her use of a private server.

The assault on the US consulate, which occurred while Clinton was secretary of state, killed four Americans in all, including Washington's ambassador to Libya Christopher Stevens

"It is highly probable, given defendant Clinton's history of reckless handling of classified information, that defendant Clinton, as secretary of state, sent and received information about ambassador Christopher Stevens and thus the US Department of State activities and covert operations that the deceased were a part of in Benghazi, Libya," said the text of the lawsuit filed in the US District Court in Washington, DC.

"As a direct result of defendant Clinton's reckless handling of this classified, sensitive information, Islamic terrorists were able to obtain the whereabouts of ambassador Christopher Stevens and thus the US State Department and covert and other government operations in Benghazi, Libya and subsequently orchestrate, plan, and execute the now infamous September 11, 2012 attack."