Iran said the Ukrainian airliner that crashed outside of an airport in Tehran, killing all 176 people on board, was shot down unintentionally by its armed forces.

Iranian officials had initially denied claims by Western officials that the Boeing Co. 737-800 jet was downed by a missile system fired by Iran, possibly by mistake.

The single-aisle jet crashed Wednesday four hours after Iran had launched military strikes against the U.S. in Iraq in retaliation for the killing of a top general, and the Middle Eastern state was on high alert for a potential U.S. response.

The Ukraine International Airlines plane approached a sensitive military base operated by the Islamic Revolutionary Guard Corps and was downed due to “human error,” Iran’s general staff of the armed forces said in a statement on state television early Saturday local time.

The armed forces detected greater U.S. air activity and U.S. warplanes on its radar after the Iranian strikes on American forces in Iraq, the statement said.