A U.S. military officer says improved security in Iraq is "fragile and far from irreversible," hours after a deadly explosion near a U.S. military patrol outside Baghdad's heavily fortified Green Zone.
Rear Admiral Gregory Smith told reporters extremists still have the will and capacity to cause major loss of life and damage to property.
Smith spoke of "multiple military and civilian casualties" from Wednesday's roadside explosion, without releasing further details.
Iraqi security officials say the blast killed two civilians and wounded three.
The U.S. embassy and some Iraqi government offices are located in the Green Zone.
In other news, a powerful Sunni Muslim group in Iraq says Iraqi security forces have seized the group's Baghdad headquarters. The Association of Muslim Scholars said on its Web site that soldiers moved into the Um al-Qura mosque in a Sunni district in Baghdad and ordered the occupants out.
The group has been known to support anti-U.S. insurgents in Iraq.
Separately, the U.S. military reported that three American soldiers were killed Tuesday in separate incidents in northern Iraq.
The military also said Iraqi Special Forces detained several extremists, including two alleged al-Qaida leaders, during separate raids on Monday in areas around Baghdad, and in the northern city of Taji.
Meanwhile, police say two people were killed and six wounded in a suicide bombing at a meeting of Sunni Arab tribal leaders near the town of Iskandiriyah, south of Baghdad.
Some information for this report was provided by AFP, AP and Reuters.