Baghdad, Iraq ? Iraqi civilian deaths have fallen in Baghdad in the two months since the Feb. 14 start of the U.S.-led offensive, according to an Associated Press tally.

Outside the capital, however, civilian deaths are up as Sunni and Shiite extremists shift their operations to avoid the crackdown.

And the sweeps have taken a heavy toll on U.S. forces: Deaths among American soldiers climbed 21 percent in Baghdad compared with the previous two months.

Since the crackdown began Feb. 14, U.S. military officials have spoken of encouraging signs that security is improving in the capital but have cautioned against drawing any firm conclusions until at least the summer.

Figures compiled by the AP from Iraqi police reports show that 1,586 civilians were killed in Baghdad between the start of the offensive and Thursday.

That represents a sharp drop from the 2,871 civilians who died violently in the capital during the two months that preceded the security crackdown.

Outside the capital, 1,504 civilians were killed between Feb. 14 and Thursday, compared with 1,009 deaths during the two previous months, the AP figures show.

“We know this increased security presence and cooperation from the people is having an impact in Baghdad,” U.S. military spokesman Maj. Gen. William C. Caldwell said this week. “It is a good beginning, but it is not nearly enough. The violence across the rest of Iraq remains at unacceptable levels.”

The Baghdad crackdown was designed to provide the Iraqi government with what U.S. officials call a “secure platform” and to buy time for the country’s religious and ethnically based political parties to agree on key reforms.

So far there has been little progress on that front.

Sunni and Shiite militants remain a potent force, regardless of whether they are slaughtering civilians in the capital at the previous rate.

It is unclear why deaths outside Baghdad have increased. However, U.S. military officials say both Sunni and Shiite extremists left Baghdad ahead of the crackdown, instead stepping up their operations in a belt of communities around the capital.

The rise in deaths outside Baghdad also may be a result of clashes in Anbar province between al-Qaida extremists and Sunni tribes that have broken with the extremist movement.