Four Americans killed in Iraq last week while working for a private security firm may have been lured into an ambush by people they thought were members of the Iraqi Civil Defense Corps (search), company officials said.

The men were working for Moyock, N.C.-based Blackwater Security (search) when their vehicle was hit by rocket-propelled grenades March 31 in Fallujah. Their bodies were mutilated and burned, and two were hung from the framework of a bridge.

Patrick Toohey (search), Blackwater's vice president for government relations, told The New York Times that the workers were led into an ambush by men they had believed were members of the defense corps.

Toohey said Iraqis had promised the Blackwater-led convoy safe passage through the city but instead suddenly blocked the road, preventing any escape from waiting gunmen.

"The truth is, we got led into this ambush," Toohey told the paper for a story published Friday. "We were set up."

Two senior Pentagon officials said Thursday they could not confirm that conclusion, and a separate military inquiry was continuing.

Blackwater spokesman Chris Bertelli said Friday the company does not yet know whether the attackers actually were members of the civil defense corps.

The company's investigators believe they know what happened during the attack, "but we just don't have information that speculates on the motivation behind their movements," he said.

Bertelli declined to say what changes the Blackwater staff in Iraq have made since the killings.

"It's certainly safe to assume anything learned in the last week and a half has been applied," he said.

Blackwater employs about 450 people in Iraq, providing security for supply convoys, buildings used by occupation forces and L. Paul Bremer (search), the nation's top U.S. administrator.