WASHINGTON (CNN) -- Some private security guards hired to protect the U.S. Embassy in Afghanistan say their contractor has allowed widespread mistreatment, sexual activity and intimidation within their ranks, according to the watchdog group Project On Government Oversight (POGO).

A spokeswoman for watchdog group POGO said hazing at a camp for security guards went "well beyond partying."

The group sent a letter to Secretary of State Hillary Clinton on Tuesday, and briefed reporters on its findings, which it said are based on e-mails and interviews with more than a dozen guards who have worked at the U.S. compound in Kabul.

The company -- ArmorGroup, North America -- has a security contract with the State Department to provide services through July 2010, and has been cited several times for shortcomings in the security required by the contract.

A U.S. Senate panel two months ago was critical of the State Department for not closely supervising ArmorGroup, after a series of warning letters from the State Department in the year leading up to the panel's inquiry.

When CNN contacted Wackenhut, the corporate parent of ArmorGroup, a spokesperson there said the company would have a response Wednesday.

The U.S. Embassy said Wednesday it was taking the allegations very seriously.

"Nothing is more important to us than the safety and security of all Embassy personnel -- Americans and Afghan -- and respect for the cultural and religious values of all Afghans," it said in a statement.

"We have taken immediate steps to review all local guard force policies and procedures and have taken all possible measures to ensure our security is sound." Should initiation rituals such as hazing be allowed? Sound off below

POGO says two weeks ago it began receiving whistleblower-style e-mails, some with graphic images and videos, that are said to document problems taking place at a non-military camp for the guards near the U.S. diplomatic compound in Kabul.

"This is well beyond partying," said Danielle Brian, POGO's executive director, after showing a video of a man with a bare backside, and another man apparently drinking a liquid that had been poured down the man's lower back.

She told CNN that ranking supervisors were "facilitating this kind of deviant hazing and humiliation, and requiring people to do things that made them feel really disgusted." Watch claims that alleged hazing at the U.S. Embassy pose a threat to security »

"This is not Abu Ghraib," she said, referring to images and videos of abuse by U.S. military troops against prisoners held at a facility in Iraq. "We're not talking about torture," she continued, "we are talking about humiliation," by supervisors causing a breakdown of morale, and a "total breakdown in the chain-of-command."

In the letter POGO sent to Clinton, Brian wrote that the problems are "posing a significant threat to the security of the Embassy and its personnel."

Among the recommendations from the group: immediate military supervision of the private security guards, a review of whether the contract should be revoked, and consideration as to whether government forces should replace private security in a combat zone.