BAGHDAD, Oct. 7 — A completed Iraqi government inquiry found that employees of the American security company Blackwater USA shot unprovoked at Iraqi civilians at a downtown traffic circle three weeks ago, an episode that killed 17 people and wounded more than 20 others, a government spokesman said Sunday.

The four-vehicle Blackwater convoy, which had stopped at Nisoor Square on Sept. 16 to seal off traffic for another convoy carrying State Department officials, “wasn’t even hit by a stone,” much less hostile gunfire when Blackwater guards began shooting at unarmed civilians, government spokesman, Ali al-Dabbagh, said.

Also Sunday, a joint commission of American and Iraqi senior officials convened here for the first time to look into ways to improve interactions between armed contractors and Iraqis they encounter in the course of transporting American diplomats. One of the main goals of the meeting, between Patricia A. Butenis, the embassy’s deputy chief of mission, and the Iraqi defense minister, Abdulqadir Mohammed Jassim, was to improve procedures to avoid the use of deadly force, and to ensure contractors “do not endanger public safety,” a statement from the American Embassy said.

The meeting occurred on a day in which a series of car bomb attacks in the capital killed at least nine people, apparently all civilians, officials said. One of the bombings occurred near the Iranian embassy and killed three people, Iraqi officials said.