The security chief at the US State Department, Eric Boswell, has resigned from his post following a scathing official inquiry into the 11 September attack on the US mission in Benghazi.

Three other officials have been relieved of their duties

State Department spokeswoman Victoria Nuland said in a terse statement that Mr Boswell had resigned with immediate effect as assistant secretary of state for diplomatic security.

Ms Nuland said the three other officials, had all been put on administrative leave "pending further action".

An official panel that investigated the incident concluded that the Benghazi mission was completely unprepared to deal with the attack, which killed US Ambassador Christopher Stevens and three other Americans.

Ms Nuland said in her statement, that "The Accountability Review Board identified the performance of four officials, three in the Bureau of the Diplomatic Security and one in the Bureau of [Near Eastern] Affairs."

US Secretary of State Hillary Clinton accepted Mr Boswell's decision to resign, the spokeswoman said.

Earlier, a US official who spoke on condition of anonymity said Mr Boswell, one of his deputies, Charlene Lamb, and a third unnamed official had been asked to resign.

The Associated Press first reported that three officials had resigned.

The Benghazi incident appeared likely to tarnish Mrs Clinton's four-year tenure as US Secretary of State, but the report did not fault her specifically and the officials who led the review stopped short of blaming her.