A suicide bomber has blown himself up at a military recruiting centre in Baghdad, killing at least 21 people.
The attack came as Iraqi troops continued their bid to retake two cities overrun by al Qaida militants.
The blast struck as an international rights group warned of the apparent use of indiscriminate mortar fire in civilian areas by Iraqi forces in their campaign to reassert control over the cities of Fallujah and Ramadi.
Al Qaida-linked fighters overran parts of both cities in the Sunni-dominated Anbar province last week, seizing control of police stations and military posts, freeing prisoners and setting up their own checkpoints.
Iraqi troops, backed by pro-government Sunni militiamen, since have been clashing with the fighters and carrying out air strikes against their positions in an effort to reassert control of the cities.
Tribal leaders in Fallujah, 40 miles (65 km) west of Baghdad, have warned al Qaida fighters there to leave to avoid a military showdown.
The United States, whose troops fought bloody battles in Fallujah and Ramadi, has ruled out sending American troops back in but has been delivering missiles to help bolster Iraqi forces, with more on the way.
Vice President Joe Biden has spoken to Iraqi Prime Minister Nouri al-Maliki twice this week, voicing support for his government's efforts to regain control of the cities and urging him to continue talks with local, tribal and national leaders.
Iran, too, is watching the unrest with alarm as it shares American concerns about al Qaida-linked militants taking firmer root in Iraq. It has offered to supply military equipment and advisers to help fight militants in Anbar should Baghdad ask for assistance.
Human Rights Watch said today that Iraqi forces appear to have used mortar fire indiscriminately in civilian areas in recent days in their effort to dislodge militants in Anbar, and that some residential areas were targeted with mortar shells and gunfire even though there was no signs of an al Qaida presence in those specific areas.
The New York-based group said its allegations were based on multiple accounts provided by Anbar residents.
It also warned that a government blockade of Ramadi and Fallujah is limiting civilian access to food, water and fuel, and that "unlawful methods of fighting by all sides" has caused civilian casualties and major property damage.
The warning came a day after the United Nations and the International Committee of the Red Cross voiced concerns about growing humanitarian threats in the area as food and water supplies start to run out.
Emergency shipments of food, water, blankets and other essential items have begun reaching families displaced by the fighting in Anbar, the UN said today.