Iraqi and U.S. forces are stepping up joint operations in Baghdad as part of a new security crackdown on sectarian and insurgent violence.
A U.S. military spokesman, Lieutenant Colonel Scott R. Bleichwehl, says Operation Law and Order conducted searches and clearing operations at multiple locations across Baghdad Thursday.
Troops also set up new checkpoints and searched vehicles.
Another U.S. military official, Lieutenant Colonel Christopher Garver, told Reuters news agency a plan to close Iraq's borders with Syria and Iran for 72 hours went into effect late Wednesday.
Despite the clampdown, three car bombs killed at least seven people in the capital Thursday.
In northern Iraq (south of the city of Kirkuk), three off-duty guards of Foreign Minister Hoshyar Zebari were killed when gunmen ambushed their car.
Zebari, a Kurdish politician, was not with the guards when the gunmen attacked.
In other news, Iraq's President Jalal Talabani said Thursday that some members of Iraq's biggest Shi'ite militia, the Mahdi Army, have been ordered by the militia's leaders to leave Iraq temporarily. Mr. Talabani said the move was made so the Baghdad security operation can succeed.
The Mahdi Army is loyal to the radical Shi'ite cleric Moqtada al-Sadr.
Also Thursday, an advisor to Iraqi Prime Minister Nouri al-Maliki confirmed the U.S. assertion that the cleric is in Iran. Sami al-Askari said the Shi'ite leader had traveled to Iran for a short visit. But he denied the characterization that Sadr fled Iraq.
Meanwhile, the U.S. military said seven U.S. troops have been killed in a series of incidents since Tuesday.
Some information for this report was provided by AFP, AP and Reuters.