WASHINGTON (CNN) -- The State Department's chief of diplomatic security has resigned amid scrutiny of the use of private military contractors to guard the department's staff in Iraq, a spokesman said Wednesday.

Richard Griffin testifies before a House committee looking into private security contractors earlier this month.

Richard Griffin, a 36-year career official, gave no explanation for his decision in his resignation letter to President Bush.

"I am grateful that I had the opportunity to serve as the assistant secretary for the Bureau of Diplomatic Security, whose brave men and women serve on the front lines of the Global War on Terror," he wrote in his resignation letter, a copy of which was obtained by CNN.

"Without their courage and commitment, the State Department could not possibly carry out its foreign policy mission."

Secretary of State Condoleezza Rice accepted Griffin's resignation, State Department spokesman Sean McCormack said.

Griffin's decision to step down follows weeks of investigations into the September 16 killings of Iraqi civilians by Blackwater USA, a North Carolina-based firm hired by the State Department to protect American diplomats in Baghdad.

Meanwhile, a survivor of the September 16 incident told CNN on Wednesday that he and a number of other victims were summoned to a meeting with U.S. Embassy officials and were offered money.

Mohammed Abdul Razzaq, whose 9-year-old son died, said the embassy offered him $12,500 -- which he said he refused because "they didn't acknowledge their crime."

"Don't they need to acknowledge my son's blood first so I can forgive them? Now I can't. How can I take compensation and they never acknowledge the crime?" he said.

The father is demanding a formal apology from Blackwater CEO Erik Prince, prosecution of those responsible for his son's death and political asylum in the United States so he can pursue the case in American courts.

Another survivor, taxi driver Sami Hawas, told CNN he received $7,500 from the embassy, a payment he described as "aid." Hawas was shot a number of times in the back and leg.

He said he is unable to work now and complained about the high cost of medication. He took the money, he said, because he needs help paying for medical treatment and supporting his family. "Even if they compensate me with millions, it will not make up for the lost blood and the pain I live every day," he told CNN.

U.S. Embassy spokeswoman Mirembe Natango said the payments were "part of a standard procedure" and would continue.

She described them as "short-term and speedy aid and support" but said they were not an admission of guilt. She said those receiving the money do not waive any right to future compensation.

The State Department and the FBI are conducting their own investigation into the killings, and a joint U.S.-Iraqi commission is reviewing the results of both probes.

Prince has said that Blackwater guards came under fire while protecting a State Department convoy and acted properly in self-defense. Watch Blackwater chief talk about his company »

But Iraqi authorities have called the killings "premeditated murder" and demanded Blackwater leave Iraq.

A State Department report of its own operations, released Tuesday, found lax oversight of security contractors, who are under the supervision of the Bureau of Diplomatic Security.

It recommended tightening the rules of engagement for contractors to bring them in line with those used by the U.S. military, and Rice appointed a top U.S. diplomat to oversee all security operations in Iraq.

Blackwater is the most prominent of the military contractors working in Iraq, where an estimated 25,000 private contractors guard diplomats, reconstruction workers and government officials. Company officials urged subscribers to its e-mailed newsletter Wednesday to help fight its public-relations battle.

"In this tumultuous political climate, Blackwater Worldwide has taken center stage, our services and ethics aggressively challenged with misinformation and fabrications. Letters, e-mails and calls to your elected congressional representatives can and will create a positive impact by influencing the manner in which they gather and present information," the company wrote.

The message, titled "A Request for Your Support," urged readers to contact members of Congress "and tell them to stand by the truth." It recommended that constituents emphasize that the company hires U.S. military veterans and the fact that no one under Blackwater's protection has been killed in Iraq. It also asked that supporters stress what the company termed the "cost efficiency" of its services, for which the State Department has paid more than $800 million since 2004.

Blackwater spokeswoman Anne Tyrrell said the company had received "hundreds of positive responses" to its appeal by Wednesday afternoon.

The contractors are immune from prosecution under Iraqi law, under an order issued by the American-led occupation government in 2004. Iraq's government has agreed to ask the country's parliament to consider changing that directive, an adviser to Prime Minister Nuri al-Maliki told CNN on Wednesday. E-mail to a friend

CNN's Jomana Karadsheh, Elise Labott, Ingrid Formanek, Jim Clancy and Saad Abedine contributed to this report.

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