Aftermath of an attack on a bus carrying pilgrims
Iraqi police say 36 people have been killed in bomb attacks targeting Shia Muslims.
In one attack, 30 people died near the northern city of Mosul when a car bomb exploded outside a mosque during a funeral service.
In Baghdad three bombs killed six people returning from a pilgrimage.
The attacks come as Shia Muslims across the country are marking one of their biggest religious holidays.
Iraq has seen frequent sectarian strife between its Shia and Sunni Muslims.
The mosque attack near Mosul - which is about 400km (250 miles) north-west of Baghdad - took place in a village named by Reuters news agency as Shreikhan.
It killed 30 people and wounded at least 61, and police said the number of casualties was likely to rise.
Mosul is still one of the most troubled cities in Iraq, a place where Sunni insurgency is still believed to be strong.
US and Iraqi officials have described the city as al-Qaeda in Iraq's last major urban stronghold in Iraq.
City authorities have urged citizens to donate blood and appealed for construction vehicles to lift debris trapping victims of the attack, according to Reuters.
"I was in the house when this explosion happened," said eyewitness Khalil Qasim, 19, speaking through his tears.
"I hurried to the mosque to search for my father in the ruins... I found him seriously wounded, and took him to hospital, but he died."
News agencies report that most people in the village are from Iraq's ethnic Turkmen community and Shia by religion.
Turkmens, who also count Sunnis and Christians among their number, are a minority in Mosul, a city of about 1.8 million people which is mainly populated by Sunni Arabs.
In Baghdad, six Shia pilgrims were killed in roadside bomb explosions. They were returning from Karbala, a holy city south of Baghdad.
They had been among hundreds of thousands of Shia pilgrims who gather in Karbala to mark the birth of Mohammed al-Mehdi - the 12th and last Shia Imam, known as the Hidden Imam.
These pilgrims have often been targeted by attacks in the past.
Iraqi pilgrims gather in Karbala
More than 20,000 Iraqi police have been deployed to protect them.
Many Iraqis say the government has yet to prove it is in full control of security.
The BBC's Natalya Antelava in Baghdad says the government is accusing Sunni insurgents linked to al-Qaeda of trying to reignite sectarian tensions in the country.
But while the majority of attacks in recent days have been aimed at Shia communities, some Sunnis have also been targeted, our correspondent says.
Last Friday, a series of apparently co-ordinated bombs outside five Shia mosques in Baghdad killed at least 29 people and injured more than 130.
But just two days ago a bomb killed three and wounded many more in one of Baghdad's predominantly Sunni neighbourhoods.