At least 12 people have been killed and 132 wounded by a huge explosion in a block of flats in the northern Iraqi city of Mosul, officials have said.
Gen Abdul Kareem al-Jubouri said the blast followed a raid on a weapons and explosives cache in the building and that nearby homes were also destroyed.
Women and children are said to be among the victims of the blast in the city, 390km (240 miles) north of Baghdad.
The ethnically mixed city 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.
Many Sunni insurgent groups are believed to have reacted by transferring their bases of operations to other provinces north of the capital.
Witnesses described Wednesday's explosion in Mosul as one of the biggest explosions they had ever heard, and said a huge plume of spoke had risen above the city.
Gen Jubouri, the head of the operations room at police headquarters in Mosul, said Iraqi security forces had launched a raid on a block of flats at 1630 (1330 GMT) after being told that weapons and explosives had been hidden inside.
Another five people were killed by a car bombing in nearby al-Dibis
The commander of the US military in northern Iraq, Maj-Gen Mark Hertling, said the Iraqi forces had accidentally detonated a roadside bomb they found inside, which then triggered a "massive secondary" explosion.
Explosive experts sent to the scene of the blast estimated that 15 tonnes of ordnance had been hidden inside by militants, he added.
The explosions caused the three-storey building to collapse and badly damaged several adjoining houses.
"There are still people trapped inside the blast site and under rubble," Gen Hertling told Reuters news agency.
Elsewhere in northern Iraq, at least five people were killed and 11 wounded by a car bomb attack in a market place in the town of al-Dibis, about 50km (31 miles) north-east of Kirkuk, police said.
Earlier, the US military said its forces had killed 10 militants in an operation targeting al-Qaeda in Iraq north of the town of Baquba in Diyala province.
Coalition forces used air support in the operation, in which supplies of weapons were also recovered, a statement said.
Five militants were killed in an operation in the same area on Tuesday, it added.