Three US State Department officials resigned under pressure on Wednesday, less than a day after a damning report blamed management failures for a lack of security at the country's diplomatic mission in Benghazi, Libya, where militants killed the US ambassador and three other US citizens on Sept 11.

An administration official said Eric Boswell, the assistant secretary of state for diplomatic security, Charlene Lamb, the deputy assistant secretary responsible for embassy security, and an unnamed official with the Bureau of Near East Affairs had stepped down. The official spoke on condition of anonymity because he wasn't authorized to discuss personnel matters publicly.

The report said poor leadership in both bureaus had left the post underprotected.

"Systemic failures and leadership and management deficiencies at senior levels within two bureaus" resulted in a security level that was "inadequate for Benghazi and grossly inadequate to deal with the attack that took place," according to the report, released on Tuesday by the independent Accountability Review Board.

Security at the mission and the deaths of the US citizens became political issues, as Republicans accused the Obama administration, and especially UN Ambassador Susan Rice, of playing down the possibility that it was a terrorist attack. Rice eventually withdrew her name from consideration to replace Hillary Clinton as secretary of state during President Barack Obama's second term.

Rice had appeared on numerous TV talk shows after the attack and linked it to an anti-Islamic film made in the United States. Her comments came after evidence already pointed to a militant attack.

The review board was led by Thomas Pickering, a retired ambassador, and Mike Mullen, a retired admiral and former chairman of the Joint Chiefs of Staff. They testified in closed sessions before frustrated lawmakers on the House Foreign Affairs Committee and the Senate Foreign Relations Committee.