The police chief of Mosul was seriously wounded in an explosion on Thursday as he toured the scene of a huge blast a day earlier which had killed at least 20 people in the northern Iraqi city, police said.

The cause of the latest blast which wounded Brigadier-General Salih Mohammed Hasan was not immediately known, police said. One of Hasan's bodyguards was killed and another five wounded, they said.

Rescuers were still digging through the rubble in search of survivors from Wednesday's huge blast, blamed by U.S. military commanders on Sunni Islamist al Qaeda, which also wounded 150.

That blast in a house used by militants to store weapons and tonnes of explosives also destroyed or badly damaged 35 homes.

U.S. military commanders have identified ethnically and religiously mixed Mosul, 390 km (240 miles) north of Baghdad, as al Qaeda's last major urban stronghold.

Al Qaeda fighters have regrouped there after being driven out of former strongholds in western Anbar province and from around Baghdad during security crackdowns last year.