Two bomb attacks in the Iraqi capital, Baghdad, have killed at least 40 people, police said.
The group of Shia pilgrims had just arrived back in Baghdad
At least 30 people died in the Karrada district when a car bomb exploded near a truck carrying Shia pilgrims.
In a separate incident, a suicide bomber blew himself up on a minibus in eastern Baghdad, killing 10 people.
The latest violence comes a day after Baghdad hosted a conference on security, attended by world powers including the US, Syria and Iran.
In Karrada, a car bomber drove into a truck that was bringing about 70 men and boys home from the holy city of Karbala, south of Baghdad.
Hundreds of thousands of pilgrims had gone to Karbala to mark the Arbaeen ceremony, one of the holiest events in the Shia calendar.
"I blame the government," the Associated Press news agency quoted one man injured in the blast as saying.
"They didn't provide a safe route for us even though they knew we were targets for attack."
Last week, in the run-up to the ceremony, scores of pilgrims were killed in bomb and gun attacks across Iraq.
Sunday's separate suicide attack happened in Baghdad's Shia stronghold of Sadr City.
Both of these attacks appear to have been aimed at killing Shia civilians, as has been the case with most of the recent bomb outrages, says the BBC's Jim Muir in Baghdad.
These have continued virtually unabated despite the current security surge by US and Iraqi government forces in Baghdad.
Mr Maliki told conference delegates Iraq needed help
The Shia militias have stood down in deference to that security plan but their compliance is bound to be strained by these continuing highly provocative attacks on their community, our correspondent says.
In the northern city of Mosul, three guards died in a blast at an office of the country's largest Sunni Arab political party, the Iraqi Islamic Party. Police said a fourth body was believed to be that of a suicide attacker.
On Saturday, Iraqi Prime Minister Nouri Maliki appealed to Iraq's neighbours to help tackle the sectarian and insurgent violence.
The one-day conference brought together envoys from the US, Iran and Syria for the first time in years.
The US blames Iran and Syria for stoking the violence, but the meeting was said to be constructive and positive.
Speaking on Sunday, a spokesman for the Iranian foreign ministry, Mohammad Ali Hosseini, called it a good first step.
"If another conference at foreign ministers level was held in Baghdad there could be more hope that a positive trend has started that will go on," he said.