More than a dozen bomb attacks in and around Baghdad on Sunday left at least 19 Iraqis and two American soldiers dead and more than 80 other people wounded.
The series of attacks comes just days after blasts against police in a tense northern city killed 29 people, with just months to go before all US forces must withdraw from Iraq amid questions over whether local security forces are up to the task of maintaining stability in the war-wracked country.
A total of 13 roadside bombs, three vehicles packed with explosives, one magnetic "sticky bomb" and one suicide attacker struck in the spate of morning blasts on Sunday, although it was not immediately clear to what extent, if any, the violence was coordinated.
The deadliest attack saw 12 people killed and 23 wounded in a suicide bombing in the town of Taji, 25 kilometres (15 miles) north of the capital, an interior ministry official said, on condition of anonymity.
A defence ministry official put the toll at 14 dead and 30 wounded in Taji.
A car bomb had initially gone off at around 9:00 am (0600 GMT) in the town and when residents and ambulance crews arrived at the scene, the suicide bomber blew himself up, causing the casualties, the interior ministry official said.
Among the victims were eight police killed, while four policemen and three soldiers were wounded.
The interior ministry official said the initial car bomb had exploded as a US army convoy was passing through Taji, but an American military spokesman said he had received "no indication" of any such attack.
Signup to our newsletter and follow us on Facebook and Twitter!
Also on Sunday, two American soldiers were killed, a US army statement said, in what an Iraqi security official said was a roadside bombing in the capital's western outskirts.
"Two US service members were killed Sunday while conducting operations in central Iraq," the American statement said, without giving any further details about the incident or the soldiers.
An Iraqi interior ministry official said two US soldiers were killed and three others wounded when the convoy they were in was struck by a roadside bomb.
Some 45,000 American troops remain stationed in Iraq and while they are mostly tasked with training and equipping their local counterparts, they also take part in joint counter-terror operations.
All US forces must withdraw from Iraq by the end of the year, according to a security pact with Baghdad.
Prime Minister Nuri al-Maliki called for a national dialogue with rival blocs earlier this month on whether or not to extend the US troop presence, and several top US officials have passed through Baghdad to press Baghdad to decide soon whether it wants an extension.
On Sunday, senior Kurdish defence official Jabbar Yawar called for American soldiers to stay past the year-end deadline, voicing rare support for a US military presence beyond 2011.
A dozen other roadside bombs, two car bombs and one "sticky bomb" killed seven people and wounded 61 in several other incidents across the Iraqi capital on Sunday.
The violence comes a day after seven people were killed in attacks in the northern province of Kirkuk, further raising tension in the oil-rich region after three bombings killed 29 people in Iraq's deadliest day since late March.
Violence is down dramatically in Iraq from its peak in 2006-7, but attacks remain common. A total of 211 Iraqis were killed in violence in April, according to official figures.