BAGHDAD - An Iraqi official conceded Sunday that Blackwater USA's exit would create a "security vacuum" in Baghdad and said U.S. and Iraqi officials were instead working on revamping regulations governing private security companies after a deadly shooting of civilians.

The killing of at least 11 civilians allegedly involving Blackwater guards near a square in central Baghdad has thrown a spotlight on the practices of foreign security contractors who have long angered Iraqis by their aggressive behavior in protecting Western diplomats and other dignitaries.

The North Carolina-based company has insisted that its guards came under fire and shot back only to defend themselves.

Following the Sept. 16 Nisoor Square shooting, the Interior Ministry banned Blackwater from operating in Iraq but rolled back after the U.S. agreed to a joint investigation. The company resumed guarding a reduced number of U.S. convoys on Friday.

But officials said new rules have to be put in place to govern the behavior of the security companies.

"If we expel this company immediately there will be a security vacuum that will demand pulling some troops off the battlefield," Tahseen Sheikhly, a civilian spokesman for the seven-month-old offensive against militants in Baghdad and surrounding areas. "This will create a security imbalance in securing Baghdad."

He said a joint U.S.-Iraqi committee was studying the framework of operations for private security companies who have largely operated without oversight since the war began in March 2003.

That committee was separate from an investigation being conducted into the incident itself amid several conflicting accounts from Iraqi officials and witnesses about what happened.

The U.S. military also said Iran continues to send advanced weaponry to militants Iraq despite Tehran's assertion it is not fueling the violence but trying to promote stability in its wartorn neighbor.

An American soldier was killed Saturday and another wounded when a powerful roadside bomb hit their patrol in eastern Baghdad, the military said.

Military spokesman Rear Adm. Mark Fox denied an Iranian detained by U.S. forces on Thursday was a businessman, saying he was a member of an elite force of the Iranian Revolutionary Guards who was smuggling bombs into Iraq, including armor-piercing explosively formed penetrators known as EFPs.

"In recent months we have seen Iran smuggle advanced weaponry into Iraq," Fox said, citing rocket-propelled grenades, EFPs, 240 mm rockets and a surface-to-air missile as among the weapons found that have been linked to Iran.

Tehran, meanwhile, said it was reconsidering whether to hold another round of talks with the United States on Iraq after the arrest.

"For another round of negotiations to take place, we have to review this event that has taken place," Iranian Foreign Ministry spokesman Mohammad Ali Hosseini told reporters in his weekly news briefing.

Hosseini said the man, who he identified as "Mr. Farhadi," was in charge of border transactions in the western Iranian province of Kermanshah and went to Iraq on an official invitation. He said Iran expects the Iraqi government to provide security for Iranian nationals there.

"Occasionally Americans do this sort of operation or abduction, which is against international norms," he said. "This U.S. behavior would affect Iran-Iraq relations."

Iraqi President Jalal Talabani, a Kurd, has demanded that the Americans release the Iranian who was detained in a raid in the northern Kurdish city of Sulaimaniyah.

The demand added new pressure to U.S.-Iraqi relations already strained over the Blackwater allegations.

Blackwater is one of three private security firms employed by the State Department to protect its personnel in Iraq, and a decision to force it to pull out would create tremendous difficulties for the U.S. government. There are 48,000 of the private security contractors in Iraq, according to the Government Accountability Office.

The two other firms, both of which are headquartered in the Washington, D.C., suburbs, are Dyncorp, based in Falls Church, Va., and Triple Canopy, based in Herndon, Va.

It is doubtful that foreign security contractors could be prosecuted under Iraqi law. A directive issued by U.S. occupation authorities in 2004 granted contractors, U.S. troops and many other foreign officials immunity from prosecution under Iraqi law. Security contractors also are not subject to U.S. military law under which U.S. troopers face prosecution for killing or abusing Iraqis.

Iraqi officials have said in the wake of the Nisoor Square shooting that they will press for amendments to the 2004 directive.

"Iraqi criminal law should be activated on Iraqi soil against any kind of criminal activity," Sheikhly said.

But he declined to comment on statements from other Iraqi officials that the Blackwater case would be referred to Iraqi courts, pending the results of the separate committee investigations, which he said could be expected in a few days.

Interior Ministry spokesman Maj. Gen. Abdul-Karim Khalaf said Saturday that Iraqi authorities had completed an investigation into the Sept. 16 shooting in Nisoor Square in western Baghdad and concluded that Blackwater guards were responsible for the deaths.

He told The Associated Press that the conclusion was based on witness statements as well as videotape shot by cameras at the nearby headquarters of the national police command. He said eight people were killed at the scene and three of the 15 wounded died in hospitals.

Blackwater, which provides most of the security for U.S. diplomats and civilian officials in Iraq, has insisted that its guards came under fire from armed insurgents and shot back only to defend themselves.

Blackwater spokeswoman Anne Tyrrell said Saturday that she knew nothing about the videotape and was contractually prohibited from discussing details of the shooting.