At least 25 people have been killed in bomb attacks in Iraq, including blasts in markets in Baghdad and an attack by a suicide bomber in a mosque in the north.

Attacks on Sunni and Shia Muslim mosques, security forces and tribal leaders have spread since security forces raided a Sunni protest camp near Kirkuk a month ago.

Iraq has grown more volatile as the civil war in neighbouring Syria strains fragile relations between Sunni and Shia Muslims.

Tensions are now at their highest since the last US troops pulled out at the end of 2011.

Today, a suicide bomber set off his explosives in a mosque in the ethnically mixed city of Kirkuk, killing at least eight people among mourners gathered to pay respects to people killed in a bombing a day earlier.

Earlier, three car bombs exploded in busy markets in eastern and northeastern Shia districts of the Iraqi capital, killing at least 14 people and wounding 26, police said.

In a separate incident, assailants with silenced weapons shot dead a prominent Sunni tribal leader in his car in southern Baghdad and seriously wounded his driver, police said.

In the northern city of Mosul, another suicide car bomber attacked a military checkpoint, killing two soldiers and wounding three, and a separate car bomb wounded two soldiers on patrol.

No group immediately claimed responsibility for the latest violence, which followed bombings that killed more than 35 people in Baghdad and the north yesterday.

According to the United Nations, April was Iraq's bloodiest month for almost five years, with 712 people killed.