Defense Department officials have said in recent weeks that they are extending the deployments of some troops and accelerating the moves of others to ensure that they have several thousand extra troops on hand as elections approach.
Many Iraqis expect a surge in violence before then, as insurgents stage attacks to disrupt elections whose success would likely be seen as an important U.S. victory. Influential groups within the Sunni community, thought to account for about one-fifth of Iraq's population, have vowed to boycott the vote, which will choose a National Assembly that will appoint a new government and draft a constitution.
Along with insurgent attacks, a shadowy campaign of killings has continued in the Sunni-dominated regions north of Baghdad.
On Tuesday, assailants killed a Sunni cleric in the town of Muqdadiyah, about 60 miles north of Baghdad. The cleric, Ghalib Ali Zuhairi, was killed near the Thiyaba mosque, where he had gone for dawn prayers, his brother, Saeb, said in an interview. His body was riddled with as many as eight bullets, most of them to his back, the brother said.
Zuhairi was the second cleric killed in as many days. On Monday, gunmen in Mosul assassinated another prominent Sunni cleric, Faidh Mohamed Amin Faidhi.
Zuhairi and Faidhi were members of the Association of Muslim Scholars, an influential Sunni clerics group that has called for a boycott of Iraqi elections.
In Baqubah, about 35 miles northeast of Baghdad, insurgents in three cars attacked a vehicle carrying Iraqi security forces, killing three of them.
Staff writer Thomas E. Ricks in Washington and special correspondents Naseer Nouri in Baghdad and Hassan Shammari in Baqubah contributed to this report.
