The US State Department's security chief Richard Griffin resigned on Wednesday amid sharp criticism over his office's poor supervision of private security firms in Iraq in the wake of the Blackwater shooting incident.

"He submitted his letter of resignation dated today," the department's spokeswoman Julie Reside told reporters, noting that Secretary of State Condoleezza Rice had accepted his resignation.

Griffin, assistant secretary of state for diplomatic security, announced his resignation one day after Rice ordered a series of measures to boost government oversight of the private guards the department uses to protect its diplomats in Iraq.

Blackwater is a major military contractor providing security services to US State Department personnel in Iraq. Its guards protecting a State Department convoy opened fire in a crowded Baghdad square, killing as many as 17 civilians on September 16.

(Xinhua News Agency October 25, 2007)