A U.S. State Department spokeswoman says an investigation is underway into an attack on a convoy in western Baghdad on Sunday.
Details of the incident have not been confirmed. But, Iraqi police say security contractors killed nine civilians in the ensuing firefight in the Mansour district.
North of the capital, Iraqi authorities say suspected al-Qaida in Iraq fighters killed at least 14 people and wounded seven others Sunday in Muqdadiyah.
The al-Qaida-linked group had warned of a new offensive during Ramadan.
Earlier Sunday, a suicide bomber killed at least six people and wounded about 19 others at an outdoor cafe in the northern town of Tuz Khurmato.
In another development, the U.S. military says troops captured a suspected al-Qaida insurgent believed to be responsible for killing a Sunni Arab leader, Sheikh Abdul Sattar Abu Risha, last week.
Abu Risha was a key U.S. ally who organized Sunni Arab clans to fight al-Qaida in Iraq. He was killed by a car bomb Thursday in Ramadi, the provincial capital of Anbar.
A statement said the suspect, identified as Fallah Khalifa Hiyas Fayyas al-Jumayli, was captured during an operation Saturday west of Balad.
U.S.-led forces in Iraq said multi-national and Iraqi troops captured four suspected terrorists early Sunday morning in targeted raids in the capital. The military also said Iraqi National Police discovered a weapons cache, including a rocket propelled grenade launcher, in eastern Baghdad on Saturday.
Some information for this report was provided by AP and Reuters.