At least 12 people have been killed in a double suicide bombing targeting a mosque frequented by Shia worshippers in the northwest of the Iraqi capital, police said.

"Two suicide bombers wearing explosive belts blew themselves up in front of the Rasul al-Azam (mosque) in the Shuala district" of Baghdad, a police official said, adding that more than 20 people were wounded in Thursday’s blasts.

"The first suicide bomber blew himself up among the worshippers as they left" the mosque, he said.

"The second explosion targeted police forces who had arrived to treat the wounded," causing more deaths, he said.

Medical sources confirmed the death toll. Four of the victims were members of the security forces, sources said.

The blasts in the predominantly Shia neighbourhood came on the eve of a planned protest that Shia cleric Moqtada al-Sadr had called for in Baghdad and said he would personally attend.

Sadr has called on his supporters to attend protests in the capital as well as other cities to demand an end to corruption and improved public services.

Tens of thousands of his supporters are expected to take part.

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Iraq has been hit by several suicide bombings in recent months. 

Earlier this month, at least 27 Iraqi soldiers were killed in suicide car bomb attacks committed by Islamic State of Iraq and the Levant (ISIL) fighters near Ramadi, according to military sources.

On Thursday, at least 22 strikes were carried out against ISIL positions across Iraq and Syria, the US-led coalition said in a statement. 

More than 20 Iraqi civilians were killed in two air strikes on towns held by the Islamic State of Iraq and the Levant (ISIL) group in the west of Anbar province, according to military sources. 

Iraqi forces and ISIL are engaged in battles across Anbar, especially around the urban centres of Ramadi - now largely controlled by government forces - and Fallujah, which is still held by the fighters.

Source: Agencies