AL SHAMS, IRAQ — About 1,000 U.S. and Iraqi troops launched a major offensive at dawn Thursday in Diyala province, an increasingly violent zone east of Baghdad that has become a haven and training ground for Sunni Arab insurgents.
The target of the strike is an isolated landscape of farms and irrigation canals riddled with weapons caches, safe houses and training ranges, U.S. military officials said.
The insurgents, however, appeared to be well prepared for the slow-moving assault. Smoke signals and flares arced into the sky as a column of tanks and Humvees from the 3rd Heavy Brigade Combat Team, 1st Cavalry Division, pressed into an insurgents' redoubt. U.S. military officials said spotters used those techniques to warn guerrillas in the area that the U.S. and Iraqi forces were approaching.
Insurgents also had dug deep trenches into the roadways and sabotaged canal bridges to slow the troops' advance. U.S. commanders said they suspected that the obstacles were designed to divert approaching vehicles toward roadside bombs.
Four hours into the operation, an explosion ripped through the front end of a U.S. Humvee but failed to penetrate the cabin. The U.S. soldiers inside were not injured, but the wreckage blocked the road for two hours as troops salvaged the vehicle and searched for additional explosives hidden along the road.
U.S. commanders viewed the operation as an opportunity to test the 400 soldiers of Iraq's 5th Army Division.
Nonetheless, commanders kept details of the operation from their Iraqi counterparts until hours before it began, out of fear that information would leak to insurgents, said Col. David W. Sutherland, commander of the 3rd Heavy Brigade Combat Team, which assumed control of Diyala in October. Sutherland said he suspected that information from Iraqi soldiers compromised counterinsurgency operations in November and December.
Some Iraqi soldiers chafed at the secrecy around the operation, which was launched from a checkpoint south of Baqubah.
"They do not trust us," said one Iraqi soldier who identified himself as 1st Lt. Ali.
The rendezvous was a chaotic scene, with dozens of armored vehicles jammed into a checkpoint. U.S. officers shouted commands in English in an attempt to make them fall in line. Several Iraqi vehicles started off in the wrong direction.
"No, this way, this way!" shouted a U.S. soldier.
By the time the joint force swept into six villages to conduct searches, there were no military-age men to be seen.
Diyala has become a sectarian killing ground, with the number of attacks on civilians more than doubling since February. A resource-rich province with a population divided among Iraq's major ethnic and religious groups, Diyala is home to at least 50,000 former officers of the Iraqi military and has become a staging ground for Sunni Arab insurgent attacks in Baqubah, the provincial capital, and Baghdad.
U.S. military commanders acknowledged that it was difficult to root out insurgents spread over such a broad swath of sparsely populated farmland, but said they hoped to keep the insurgents off balance by disrupting training and operations.
"We will never kill or capture them all, and even if we do, there are plenty more who will take their place," Lt. Col. Andrew Poppas said. "Our success, in my view, will be based on continued presence, denying this place as a safe haven."
Despite the temporary confusion and trust issues, the Iraqi soldiers appeared eager to work with their American partners. Some sang celebratory songs in unison as they grabbed their gear and assembled near their Humvees.
Operations in the insurgent badlands of southeast Diyala are still a novelty for Iraqi troops, said an Iraqi soldier, and they relished a chance to strike back at gunmen who pepper the southernmost Diyala army outpost so often that it has been named "The Death Station."
"They are all terrorists there," said a Shiite Muslim soldier from Basra, who declined to otherwise identify himself.
Insurgent leaders are well organized and have relatively deep public support. Abu Musab Zarqawi, leader of Al Qaeda in Iraq, was killed by U.S. forces last year in western Diyala, and his group retains a strong presence in the province. Ansar al Sunna, another insurgent group, also is active. But the most well-established groups, such as the Council and the 1920 Revolutionary Army, are composed of ex-Iraqi soldiers, U.S. officials said.
Two hours after joining the Iraqi soldiers, the convoy rumbled toward Diyala's southeastern hinterlands. As they progressed, reports crackled over the radio of four more explosions, which disabled U.S. vehicles but did not injure any troops. Two more bombs were found before they were detonated.
Helicopters spotted small groups of armed men using the network of irrigation canals that crisscross the region to bypass U.S. and Iraqi ground troops. U.S. officials said they killed nine suspected insurgents and detained about nine others.