Lieutenant General Ricardo Sanchez also admitted to reporters on Thursday that Iraqi resistance attacks were increasingly getting more sophisticated and that it would take years before Iraq could maintain internal security without external assistance.
"The enemy has evolved. It is a little bit more lethal, little bit more complex, little bit more sophisticated and in some cases a little bit more tenacious," Sanchez told a news conference.
"As long as we are here, the coalition need to be prepared to take casualties. We are still fighting…we should not be surprised if one of these days we wake up to find there's been a major firefight or a major terrorist attack," he said.
Sanchez said that on average, three to six soldiers were being killed each week and around 40 injured.
His admission comes amid a stubborn Iraqi resistance, that US-led coalition troops seem unable to curb.
"The enemy has evolved. It is a little bit more lethal, little bit more complex, little bit more sophisticated and in some cases a little bit more tenacious"
US Army Commander
Sanchez described the resistance as a combination of those loyal to former president Saddam Hussein, foreign fighters, terrorists and plain criminals.
In a startling disclosure, Sanchez claimed that some members of the new Iraqi force, many of whom were recruited from the former police or army, had attacked coalition forces.
Sanchez said the resistance consisted mostly of small low-intensity attacks, but that there were increasing coordination.
"Its clear that there's a local command control that’s operating," he said.
"We are still not seeing national command and control structures, and the regional structures –there are some indications that that's beginning to evolve," the US commander said.