[Read: Iran’s only female Olympic medalist has defected from the country over “lies” and “injustice.”]

The Iranian military's statement said the plane “took the flying posture and altitude of an enemy target” as it came close to an Islamic Revolutionary Guards Corps base. It said that “under these circumstances, because of human error,” the plane “came under fire.”

The military said it would undertake “major reform in operations of all armed forces” to make sure that such an error never happened again. It said Revolutionary Guards officials had been ordered to appear on state media and give the public a full explanation.

In a statement of his own, Iran’s foreign minister, Mohammad Javad Zarif, tried to place some of the blame on the United States, saying on Twitter that the disaster was “caused by U.S. adventurism.” The military’s statement said there had been information suggesting the United States was “preparing to aerially target sensitive defense and key sites and multiple targets in our country, and this led to even more sensitive defense posture by our antiaircraft units.”

The State Department had no immediate comment late Friday about Iran’s admission of responsibility.

Suspicions that an Iranian missile had brought down the plane were raised immediately after the crash Wednesday morning — just hours after Iran fired missiles at two bases in Iraq housing American forces.

The Iranians asked the National Transportation Safety Board to help with the investigation, and the State Department granted waivers to allow the American agency to help. A senior administration official said Friday that he thought the Iranians wanted American investigators there to keep up the appearance that they did not know what had caused the crash.

The official, who spoke on the condition of anonymity because he was not authorized to discuss these matters publicly, said the Iranian military had poor command and control, and that this was reflected in what had happened with the airplane. Communications among officials and between units are often lacking, he said, and confusion can be the norm. Western analysts often overestimate the capability of parts of the Iranian military, he said.