Major John  Hall, US army spokesman, said in an email to the AFP news agency that the operations were planned and executed by Iraqi forces, with US troops taking on a secondary role. 
 
"The goal of the operation is to seek out and destroy criminal elements and terrorist threats in Diyala and eliminate smuggling corridors in the surrounding area," it said.

The religiously mixed area is strategic because it contains key supply routes to Baghdad and northern cities that need to be controlled to ensure the areas' security.
 
"It is a mini-Iraq. There are Sunnis, Shia, Kurds, Christians," Colonel Ali al-Karkhi, commanding officer of Iraqi forces in Khan Beni Saad, a town near Baquba, said in an interview last week.

Mass deployment
  
Major General Abdul Karim Khalaf, the interior ministry spokesman, had announced on July 13 that the Iraqi military would launch an assault on Diyala.
  
Earlier this month the US military said a force of 30,000 Iraqi soldiers and police were massing in Diyala and its capital Baquba, an area where fighters have carried out frequent attacks.
  
Aided by the US military and Iraqi forces, local anti-al-Qaeda groups known as Sahwa, or Awakening councils, have inflicted severe blows on al-Qaeda and other armed groups, but they continue to wage attacks in the region.
  
Several recent strikes have been carried out by female suicide bombers, with one woman killing eight people when she blew herself  up as a Sahwa patrol passed by in Baquba last week.
  
Mohammed al-Asskri, a defence ministry spokesman, said that the security operation - codenamed "Glad Tidings" - would specifically target al-Qaeda operatives and criminals.
     
The US military also says that it believes that many fighters in the area are "rogue" members of the Shia Mahdi army militia of Moqtada al-Sadr.

Baghdad pilgrimage

Meanwhile, thousands of Shia pilgrims walked throught the streets of Baghdad amid a heavy security presence after 25 people were killed by three female suicide bombers.

About one million people are expected at the Kadhimiyah shrine [AFP]
An extra 5,000 police and soldiers have been deployed and additional checkpoints set up following the attack the previous day.

About one million people were expected at the shrine in Kadhimiyah as the Shia religious ceremony marking the death 12 centuries ago of imam Mussa Kadhim came to a climax on Tuesday. 

"Despite the explosions that happened, I can see that people are united and determined to complete the visit to the Kadhimiyah  shrine," Alaa Abdul Hussein, one of the pilgrims, said.

Another suicide attack and gunfire in Iraq's northern city of Kirkuk on Monday killed at least 27 and wounded 126, as they protested against a draft provincial election law.

Thousands of Kurds in Irbil defied fears of another attack on Tuesday to gather for another demonstration.