(CNN) Part of a video of a State Department press briefing addressing secret talks between the U.S. and Iran was deliberately deleted before it was posted online, an investigation by the department's legal adviser found Wednesday.

State Department spokesman John Kirby told reporters Wednesday that an unknown U.S. official made a request over the phone to delete several minutes of a December 2013 video of the exchange between reporters and a State Department spokeswoman. The State Department routinely posts on its site the briefing that it holds nearly every day with the diplomatic press corps.

Kirby said the department technician who made the edit could not recall who requested it.

The deleted portion of the video involves questions about a previous press briefing in 2012 in which then-State Department spokeswoman Victoria Nuland denied secret talks between the U.S. and Iran about a potential nuclear deal were taking place.

After it was revealed in December 2013 that secret talks between the U.S. and Iran actually had taken place, then-spokeswoman Jen Psaki admitted the administration lied in order to protect the secret negotiations.

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