A suicide bomber blew himself up inside a Shia mosque in northern Baghdad, killing at least 14 people during evening prayers, sources say.
A further 25 people were wounded in the attack, which took place in the Sab al-Bor district on Saturday.
The attack follows others on the same day in which at least nine people were killed, also north of the Iraqi capital.
Saturday's blasts mark the latest violence in Iraq which is stoking fears of a return to full-scale sectarian war.
In Mosul, a suicide attacker set off a vehicle rigged with explosives near a police patrol on the city's southern outskirts. The explosion killed four people including a policeman, police and medical officials said.
In the ethnically mixed town of Tuz Khurmatu, which lies at the heart of the area disputed by Kurdish leaders and the Baghdad government, gunmen opened fire on another police patrol, killing three policemen and wounding a fourth, security and medical officials said.
The tract of land, which the Kurds want to incorporate over the objections of Baghdad, stretches from Iraq's eastern border with Iran to its western frontier with Syria.
Diplomats and officials say the unresolved row is one of the biggest threats to Iraq's long-term stability.
In the mostly Sunni Arab city of Tikrit, armed people fired on day labourers waiting near a grain silo, killing two and wounding four, officials said.
Iraq has suffered a surge in violence since the beginning of the year, coinciding with rising discontent among Sunnis that erupted into protests in late December.
More than 1,000 people were killed in attacks in Iraq during May, according to the United Nations, making it the deadliest month since the 2006-2007 sectarian bloodletting.