BAGHDAD - A suicide bomber blew himself up inside a Shi'ite mosque in northern Baghdad killing at least 12 people during evening prayers, police and medics said, in the deadliest of a series of attacks that claimed more than 30 lives across Iraq on Saturday.

Sectarian tensions in Iraq and the wider region have been inflamed by the civil war in Syria, where mainly Sunni Muslim rebels are fighting to overthrow President Bashar al-Assad, whose Alawite sect derives from Shi'ite Islam.

Insurgents including al Qaeda's Iraqi affiliate have been regaining ground and recruits from the country's Sunni minority, which feels sidelined since the U.S.-led invasion toppled former dictator Saddam Hussein and empowered majority Shi'ites.

"A suicide bomber blew himself up among the worshippers in the middle of evening prayer. There were bodies drenched in blood and others shouting for help while smoke filled the mosque," said a policeman at the scene.

A further 25 people were wounded in the attack, which took place in the Sab al-Bor district near Taji, 20 km (12 miles) north of Baghdad.  

Scattered attacks across the country throughout the day killed at least 22 others, around half of them in or near the northern city of Mosul, where a suicide bomber killed four people at a police checkpoint.    

In the western province of Anbar, which shares a border with Syria, militants detonated two car bombs near a checkpoint and attacked it with rocket-propelled grenades, killing five policemen.

Two people were killed when gunmen hurled a hand grenade at a gathering of labourers in Tikrit, 150 km (95 miles) north of Baghdad, and a roadside bomb near some restaurants in the centre of the capital killed two more.

More than 1,000 people were killed in Iraq in May alone, making it the deadliest month since the sectarian bloodletting of 2006-07.