In a leaked audiotape that offers a glimpse into the behind-the scenes power struggles of Iranian leaders, Foreign Minister Mohammad Javad Zarif said the Revolutionary Guards Corps call the shots, overruling many government decisions and ignoring advice. In one extraordinary moment on the tape that surfaced Sunday, Mr. Zarif departed from the reverential official line on Maj. Gen. Qassim Suleimani, the commander of the Guards’ elite Quds Force, the foreign-facing arm of Iran’s security apparatus, who was killed by the United States in January 2020.

The general, Mr. Zarif said, undermined him at many steps, working with Russia to sabotage the nuclear deal between Iran and world powers and adopting policies toward Syria’s long war that damaged Iran’s interests. “In the Islamic Republic the military field rules,” Mr. Zarif said in a three-hour taped conversation that was a part of an oral history project documenting the work of the current administration. “I have sacrificed diplomacy for the military field rather than the field servicing diplomacy.”

The recording, of a conversation in March between Mr. Zarif and an economist named Saeed Leylaz, an ally, was not meant for publication, as the foreign minister can repeatedly be heard saying on the audio. A copy was leaked to the London-based Persian news channel Iran International, which first reported on the recording and shared it with The New York Times.

On it, Mr. Zarif confirms what many have long suspected: that his role as the representative of the Islamic Republic on the world stage is severely constricted. Decisions, he said, are dictated by the supreme leader or, frequently, the Revolutionary Guards Corps.

Iran’s foreign ministry did not dispute the authenticity of the recording but questioned the motive for the leak. Saeed Khatibzadeh, a spokesman for the ministry, called it “unethical politics” and said the portion of the audio released did not represent the full scope of Mr. Zarif’s comments about his respect and love for General Suleimani.