BAGHDAD, Iraq – American aircraft mounted four strikes in Fallujah on what the American military said were safe houses used by Abu Musab al-Zarqawi’s terror network. A Sunni Muslim clerical group demanded that the Iraqi government prevent any fullscale American attack on Fallujah, hoping to muster the same public anger that forced the Marines to abandon a siege of the city last spring.

In other violence, 11 American soldiers and an Iraqi interpreter were wounded when two car bombs exploded in Samarra, a city that American and Iraqi forces have hailed as a success story since taking it from insurgents last month.

A suicide bomber in Baghdad detonated his car near an American patrol on the airport road, wounding two American soldiers and two Iraqi policemen. Mr. al-Zarqawi’s terror organization claimed responsibility for the attack, though it was not immediately possible to verify that the Internet posting was authentic.

American and Iraqi forces have stepped up operations seeking to curb insurgent violence so that Iraqi voters throughout the country can choose a new transitional government in January. The elected assembly is to draft a new constitution in a major step toward democratic rule after decades of tyranny and military occupation.

Separately, CARE International suspended operations in Iraq yesterday, a day after the aid group’s director for Iraq, Margaret Hassan, was abducted. Her family said yesterday they had received no demands from the kidnappers.

The American command said its warplanes struck more targets yesterday believed connected to Mr. al-Zarqawi’s fighters. It denied witness reports that American aircraft attacked a women teacher’s college and a house where a family of six was killed.

The Iraqi government had been negotiating with Fallujah representatives in hopes of ending the standoff in the city and allowing the Iraqi National Guard to take over security duties there. But the talks broke down last week over what the Fallujah negotiators called the “impossible condition” that the city hand over Mr. al-Zarqawi and other foreign fighters. Fallujah leaders claim Mr. al-Zarqawi isn’t there.

Also yesterday, Staff Sergeant Ivan Frederick, 38, pleaded guilty to five charges stemming from the Abu Ghraib prison scandal. Frederick, the highest-ranking soldier charged in the abuse case, is expected to be sentenced today.

In another development, two Egyptian mobile telephone engineers were released by kidnappers who abducted them from their Baghdad office last month, their employer said.