The top counter-terrorism official in the US has said that al-Qaida in Iraq is the strongest it has been since 2006.
Just hours after more than 40 people were killed in another round of ethnic violence, Matt Olsen, the head of the US National Counterterrorism Centre, told a Senate committee: "The group is exploiting increasingly permissive security environments in Iraq to fundraise, plan and train for attacks."
Al-Qaida's Iraqi branch, known as the Islamic State of Iraq and the Levant (Isis, or Isil), has drastically increased the number of attacks against the Shiite-led government in recent months, killing more than 5,000 people since April and stoking fears of an all-out civil war.
The latest attacks targeted Shiites pilgrims marking the religious ritual of Ashoura. Dozens were killed and more than 100 injured.
At least 32 people died when a suicide bomber blew himself up as pilgrims gathered in the town of al-Saadiyah, 140km (90 miles) northeast of Baghdad.
Ashoura commemorates the death of Prophet Muhammad's grandson, Imam Hussein, in the 7th-century battle of Karbala. As part of the celebrations some worshippers whip their bodies with chains and knives in grief, drenching themselves in blood during a procession.
In a separate incident, a twin bombing hit food tents set up for pilgrims passing through the city of Hafriyah on the way to Hussein's gold-domed shrine in Karbala. Nine people were killed.
No group claimed responsibility for the attacks but Shiite religious gatherings are often Isis targets as al-Qaida and other Sunni extremists consider Shiites heretics.
The influence of al-Qaida's Iraqi branch peaked in 2006 amid the chaos that followed the toppling of Saddam Hussein but was eventually curbed by US operations.
In recent months, however, Isis has regained momentum, exploiting the ongoing civil war to extend its reach into Syria.
In October, Iraqi president Nouri al-Maliki visited Washington to ask for more aid in the form of money, weapons and military trainers.