BAGHDAD, Sept. 21 — Iraq’s Ministry of Interior has concluded that employees of a private American security firm fired an unprovoked barrage in the shooting last Sunday in which at least eight Iraqis were killed and is proposing a radical reshaping of the way American diplomats and contractors here are protected.

Meanwhile, for the first time since the shootings United States embassy convoys began to leave the Green Zone today on “a very limited basis,” Mirembe Nantongo, an American Embassy spokeswoman, said in a statement. “This decision has been taken after consultation with Iraqi authorities.”

The convoys all but stopped on Tuesday, when the Iraqi government banned Blackwater USA, a company that guards all senior American diplomats here, from working in the country. But neither the statement nor another embassy official confirmed whether Blackwater was involved today, or who was providing security or where they traveled.

The official, who spoke on the condition of anonymity because of the sensitivity of the subject, conceded that it was “likely” that Blackwater was involved. There would appear to be few alternatives. The embassy could turn to State Department diplomatic security officers or another military contractor, but these options appear unlikely.