More than 8,000 police officers had also been wounded in attacks in the same period, Major General Joseph Peterson said on Friday.
Peterson said there were many Iraqi police who had "paid a great price" for their loyalty to their country.
Iraq's police force has been repeatedly targeted by armed Sunni groups and has also been widely infiltrated by Shia militias.
Peterson said that it is hard to tell how many militia members have infiltrated the police forces.
"I have no idea what the number is," said Peterson, speaking from Baghdad to reporters at the Pentagon.
"Certainly if we ask the question, they won't respond that they are associated with any militia ... It's something we continue to look for. We do ask the question."
On Wednesday, the Iraqi authorities withdrew a brigade of about 700 policemen from service in their biggest move ever to stop units linked to death squads.
About 186,000 Iraqi police have been trained, and officials expect to exceed the goal of 188,000 by 10,000 by the end of the year, Peterson said.
Currently there are 6,000 US-led forces embedded with the Iraqi police units as training teams.
Peterson said the Iraqi police are becoming better trained and more willing to stand up to insurgent attacks.
"A year ago we had a situation where a police station was attacked and policemen would run out the back door, leaving all the equipment," he said.
"That does not occur anymore."
Condoleezza Rice, the US secretary of state, left Iraq after meeting with Kurdish leaders on Friday.
Rice met the Kurdish regional president, Massud Barzani, in Arbil, the capital of the Kurdistan region, after an un-announced visit to Baghdad, the Iraqi capital.
Barzani and Rice discussed the
Kurdish oil issue
"The Kurdish people will ... certainly be better served if Baghdad and its surrounding areas are stable and democratic," Rice said.
"We had a very good discussion about the national reconciliation process and the vision of unified democratic Iraq that is stable, that is at peace and at peace with its neighbours."
Grateful for the US invasion of Iraq that overthrew Saddam Hussein, Iraq's Kurds have supported the Baghdad government's attempts to rebuild the war torn country.
But separatist tensions are never far from the surface, and fierce rows have recently erupted over the banning of Iraq's national flag in the north and the Kurdish government's determination to develop its own oil industry.
Washington fears a Kurdish declaration of independence would accelerate the possible disintegration of Iraq and knows it would be bound to anger regional ally Turkey.