Washington deployed some 275 military personnel to protect its embassy in Baghdad, the first time it has publicly bolstered the mission's security.
And it was also mulling air strikes against the militants, who are led by the militants Islamic State of Iraq and the Levant (ISIL) but include loyalists of now-executed Sunni Arab dictator Saddam Hussein.
A relative calm in Baghdad was shattered by a string of bombings that left 17 people dead, while the bodies of 18 soldiers and police were found near the city of Samarra, shot in the head and chest.
More than a week after insurgents launched their lightning assault, Prime Minister Nuri al-Maliki dismissed several senior officers, including the commander for the northern province of Nineveh, the first to fall.
Maliki also ordered that one of them face court-martial for desertion. The dismissals came after soldiers and police fled en masse as insurgents swept into Nineveh's capital Mosul, a city of two million, abandoning their vehicles and uniforms.