Two car bombs killed more than 50 people in Sunni Arab areas of Iraq on Tuesday, a sudden spasm of violence in places which had been comparatively quiet while battles raged in the Shi'ite south.
In one of the deadliest strikes in months, one car bomb killed 40 people and wounded 70 others outside a provincial government headquarters in Baquba, local capital of Diyala province north of Baghdad, police said.
Police said they expected the death toll to rise further because there were still charred bodies inside cars at the scene of the blast in the capital of Diyala. women and children were among the victims.
US forces gave an initial death toll of 20 and said three buses and five shops were destroyed.
"These acts are intended to inflict fear into the local population and are just another example of the cruelty of the anti-Iraqi insurgency," military spokeswoman Major Peggy Kageleiry said in a statement.
Medical sources said ambulances were struggling to get the wounded to hospitals because of the sheer number of victims.
A second car bomb, believed to be driven by a suicide attacker, exploded outside a restaurant in Ramadi, capital of Anbar province west of Baghdad, killing 13 people and wounding 14 others, a hospital source and police said.
Diyala, a multi-ethnic region and one of the most volatile parts of Iraq, has been the scene of operations against Al- Qaeda by US and Iraqi forces in recent months. Suspicion in the attacks will fall on Al-Qaeda, given the Sunni Arab militant group's history of using car bombs.
The strikes were a reminder of the instability rampant in the Sunni Arab areas at a time when attention has been focused on fighting in Shi'ite areas that erupted last month.
Al-Qaeda fighters have often sought sanctuary in these areas to help them blend in and take advantage of Sunni grievances.
But besides attacks on security forces and officials, they have also frequently exploded car bombs in public places to cause as much carnage as possible, irrespective of which sect bystanders are from.
Most US troops in Iraq are deployed in Sunni Arab areas, which have become quieter over the past year. But commanders say militant groups like Al-Qaeda still have the capability of staging large-scale strikes.
Tuesday's attacks could signal a new campaign of strikes by Sunni Arab militants. On Monday, a suicide attacker and two car bombs killed 18 people in northern areas where Al-Qaeda is active.
Sunni Islamist Al-Qaeda militants have regrouped in provinces north of Baghdad such as Diyala after being pushed out of Anbar and the capital by a "surge" of US forces in Iraq during the past year.
In Baghdad, fighting over recent weeks has been dominated by clashes between masked Shi'ite fighters and US and Iraqi troops. Fresh battles erupted overnight.
The US military said it had killed at least 10 fighters in Sadr City, the east Baghdad stronghold of Shi'ite cleric Moqtada al-Sadr.
Six fighters were killed in one incident involving a gunbattle and helicopter strikes, the military said in a statement. Spokesman Lieutenant-Colonel Steven Stover said US forces in a tank killed four militants in a separate incident.
Police reported at least six people killed and 26 wounded in Sadr City clashes, which have trapped frightened residents in their homes for weeks.
Fighting in Shi'ite areas in Baghdad and the south has been more intense than at any time since the first half of 2007, thrusting the Iraq war back to centre stage in the US presidential campaign.
(Additional reporting by Peter Graff, Aws Qusay and Aseel Kami; Editing by Richard Balmforth)