Car bombs hit five Shia mosques in Baghdad and the northern Iraqi city of Kirkuk just after prayers today, killing 19 worshippers and injuring another 130.
The blasts hit Shia mosques in southeast and north Baghdad while another tore the front off a mosque in Kirkuk, an ethnically mixed city of Arabs, Kurds and Turkmen 170km north of the capital.
Police and health officials said the attacks in Baghdad killed 16. Three more died in Kirkuk, where the blast left a jumble of concrete wreckage in the mosque and on the street outside.
Attacks in Iraq are still less common than during the Sunni-Shia slaughter that erupted at the height of the last war, when insurgents bombed the Shia al-Askari shrine in Samarra in 2006, provoking a wave of retaliation by Shia militias.
Al-Qaeda's local wing, Islamic State of Iraq, has vowed to keep up attacks and security officials say insurgents are regrouping in the deserts of western Iraq, invigorated by the war Sunni rebels are waging in Syria over the border.
Al-Qaeda in Iraq claimed responsibility for a wave of bombings and suicide attacks earlier this month that killed around 60 people on the 10th anniversary of the US invasion.
Sunni Islamists see Prime Minister Nuri al-Maliki's Shia-led government as oppressors of the country's Sunni minority and are targeting Shias to try to trigger the kind of inter-communal mayhem that killed thousands in 2006-07.
Iraq's government says it takes no sides in the Syrian war but its interests are often aligned with those of Shia Iran.
US Secretary of State John Kerry on Sunday pressed President Maliki to stop Iranian flights taking arms over Iraqi airspace to Syria.