Washington (CNN) The Department of Defense made an "inadvertent breach" of confidential communications between a US-Saudi citizen being detained in Iraq and his attorneys with the American Civil Liberties Union, but it has committed to steps to remedy the situation, according to a court filing Friday.

The Pentagon recorded 18 phone calls between the ACLU attorneys and their client, who is being held for allegedly fighting for ISIS, the Justice Department filing said. The unnamed man was captured in Syria last September by the Syrian Democratic Forces, a US-backed, predominantly Kurdish militia battling ISIS in the country, and was handed over to US authorities in Iraq.

The Pentagon "deeply regrets" the "inadvertent breach" of attorney-client communications, the filing said.

ACLU attorney Jonathan Hafetz said in a statement on the incident, "Confidentiality of attorney-client communications is a cornerstone of our legal system, and any violation of it is cause for serious concern. The government properly informed us that it recorded and screened our client's privileged communications, and we will hold the government to its commitment to address this breach."

The Pentagon had arranged for the prisoner's attorneys to take his phone calls from a conference room at the US Attorney's Office for the Southern District of New York instead of from Washington, DC, for their convenience, the Justice Department filing said. However, Defense Department personnel who arranged for the calls were unaware they would be recorded as part of a "routine DoD security monitoring of DoD telecommunications systems," it said.

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