The U.S. Department of State has known for decades that inadequate security at embassies and consulates worldwide could lead to tragedy, but senior officials ignored the warnings and left some of America’s most dangerous diplomatic posts vulnerable to attack, according to an internal government report obtained exclusively by Al Jazeera’s Investigative Unit.

The report by an independent panel of five security and intelligence experts describes how the Sept. 11, 2012, attack on the U.S. Special Mission in Benghazi, Libya, which left Ambassador J. Christopher Stevens and three other Americans dead, exploited the State Department’s failure to address serious security concerns at diplomatic facilities in high-risk areas.

Among the most damning assessments, the panel concluded that the State Department’s failure to identify worsening conditions in Libya and exemptions from security regulations at the U.S. Special Mission contributed to the tragedy in Benghazi. Undersecretary for Management Patrick Kennedy approved using Benghazi as a temporary post despite its significant vulnerabilities, according to an internal State Department document included with the report.