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 Human Rights Watch warned of the apparent use of indiscriminate mortar fire in civilian areas by Iraqi forces in their campaign to reassert control over 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, have since 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 west of Baghdad, have warned al Qaida fighters there to leave to avoid a military showdown.
The US, whose troops fought bloody battles in Fallujah and Ramadi, has ruled out sending US troops back in but has been delivering missiles to help bolster Iraqi forces.
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 US concerns about al Qaida-linked militants taking firmer root in Iraq.