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BAGHDAD, Jan 23 (Reuters) - A bomb attack on a residential building in Iraq's northern city of Mosul on Wednesday killed at least seven people and wounded more than 70, police said.

Witnesses said it was one of the biggest explosions they had ever heard in Mosul, part of a region where al Qaeda in Iraq militants have regrouped after being pushed out of Baghdad and western Anbar province.

The Sunni Islamist militant group is blamed for most major bombings in Iraq.

Women and children were among the victims, police said, adding that the death toll was expected to rise.

Brigadier-General Abdul Kareem al-Jubouri, head of the operations room in the Mosul police command, said police had been tipped off about a large stock of weapons at the building.

Iraqi police and soldiers were sent to the building. Just as security forces reached the building, it exploded, he said.

A huge plume of smoke rose above Mosul, 390 km (240 miles) north of Baghdad.

The U.S. military has been carrying out large-scale offensives against al Qaeda in northern provinces this month. (Writing by Dean Yates, Editing by Elizabeth Piper)

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