An Iraqi police chief has died in an apparent ambush as he toured the site of a blast that had killed at least 34 people in the northern city of Mosul.
Brig Gen Saleh Mohammed Hassan was fleeing the area after gunmen opened fire on his convoy, reports say.
The convoy was hit by an explosion that also killed two other police officers. The cause of the blast is unconfirmed.
More than 200 bystanders were hurt on Wednesday in a huge blast as troops were surrounding a block of flats.
Provincial officials increased the confirmed death toll from 20 on Thursday and said it may rise further.
"Whole families have vanished, there are still people trapped under the rubble," said council chief Hisham al-Hamdani.
The ethnically mixed city of Mosul has seen an upsurge in violence in the past year.
Correspondents say the increased violence appears to be a consequence of the offensive by US-led forces in and around Baghdad, with Sunni Arab insurgents believed to have transferred their operations further north.
Searching for survivors
The BBC's Jonny Dymond in Baghdad says that, all of a sudden, the largest and most divided city in the north appears to be on the edge.
A police statement said a suicide bomber wearing an explosives vest under an Iraqi police uniform carried out Thursday's attack, but the local military commander told the BBC it had been a roadside bomb.
Iraqi and American military forces had been clearing away the rubble from Wednesday's blast searching for bodies or survivors.
Brig Gen Hassan, the director of police for Ninevah province, was touring the area when it was ambushed by gunmen.
Dozens of buildings were damaged or destroyed in the earlier explosion when what was thought to be an arms cache levelled a three-storey apartment block in one of the poorer areas of western Mosul.
The explosion came as Iraqi troops surrounded the building following a tip-off about a suspected arms cache inside.
Separately on Thursday, a roadside bomb struck a police patrol in central Baghdad, killing two officers. Two other policemen and three civilians were wounded.