A US private security officer in Iraq, 18 Sept. 2003 file photo

Two panels made up of key Iraqi and U.S. officials are investigating a deadly incident involving Blackwater security a week ago that left 11 Iraqis dead.   

One panel seeks to resolve the widely different versions of what happened in the gun battle.  Blackwater says a convoy it was protecting was attacked and guards responded appropriately.  But some Iraqi witnesses say Blackwater started the shooting.

A second panel is reviewing the practices of the many private security companies operating in Iraq and what changes should be made in the laws that govern them.

Iraqi government official Tahseen Sheikhly told reporters the panels could reach conclusions "in a few days."

Iraqi officials initially said they would end Blackwater's work in Iraq.  But Sheikhly says the firm plays a key role by protecting U.S. diplomats and civilian officials.

"If this company left, it would leave a security vacuum, because foreign embassies and companies depend on protection by this company," Sheikhly said. "If they left immediately there would  be a security vacuum that will demand pulling some troops that work in the field."

Sheikhly spoke through a translator.

A private contractor gestures to their colleagues flying over in a helicopter, 5 July 2005 (file photo)

Meanwhile, the U.S. military again accused Iran of stirring up trouble by shipping advanced weapons to militants in Iraq, even though Teheran denies sending the deadly cargos.

U.S. military spokesman Admiral Mark Fox says an Iranian arrested Thursday in northern Iraq was part of a group that smuggles powerful explosives designed to wreck American armored vehicles and kill U.S. troops.

"When captured, the Quds force officer was posing as a businessman, in reality he is a member of ... the Quds force responsible for all operations in Iraq," Fox said.

Iraq may be getting some diplomatic help soon.  Saturday, U.N. Secretary-General Ban Ki-moon said he expects to increase the number of U.N. personnel in Iraq as soon as facilities are ready in the cities of Baghdad, Irbil and perhaps Basra

The United Nations reduced its presence in Iraq in 2003 when a bomb hit its Baghdad office killing 22 people.