WEST KARABILA, Iraq (CNN) -- U.S. Marines and Iraqi soldiers Friday battled an unseen enemy -- the handmade bombs that the the military calls improvised explosive devices -- on day seven of a major anti-insurgent offensive in northwestern Iraq.Five Marines were injured when they stepped on a pressure plate, detonating a hidden device, according to CNN's Arwa Damon, who is embedded with U.S. troops taking part in Operation Steel Curtain.Meanwhile, Arabic-language news network Al-Arabiya reported that Saddam Hussein's former deputy, Izzat Ibrahim al-Douri, has died. The report quoted a Baath Party statement.CNN has not been able to confirm the death, and previous reports of Ibrahim's death or capture have proven to be unfounded. Al-Arabiya gave no details on how or where he died. (Watch: Who is Izzat Ibrahim al-Douri? -- 1:30)Ibrahim was the most senior member of the former regime still at large and had been an insurgent leader. He is sixth on the U.S. military's list of the 55 most-wanted Iraqis, with a $10 million reward offered for his capture. (Reward offered)In northwestern Iraq, Marines are becoming frustrated because insurgents have vanished and left hidden in their wake a large number of handmade bombs.One was discovered when Marines spotted what looked like a small bunker along a main road. Inside was a switch hooked to a wireless telephone. Wires leading from the switch led to a crater beneath the road filled with artillery shells and propane tanks.Marines said the device was in a crater that had once been used to hide a bomb. The insurgents refilled the hole with explosives and covered it with asphalt.The Marines dug out the materials and detonated them in a massive explosion.Advances through western Karabila slowed to a crawl as troops picked through a minefield of handmade bombs.One Marine commander called the bombs a "very effective enemy," saying they "can lay in wait for days, months and years."Marines found two bomb-making factories a few hundred yards apart filled with supplies including electronics, explosives and wires, along with propane tanks and mortar rounds primed to explode. The troops also found sniper rifles and a vest similar to those used by suicide bombers.Thursday afternoon, a Marine was killed and an Iraqi soldier was wounded by a roadside bomb. In addition, Marines and Iraqi soldiers discovered three missiles hidden under a room filled with hay. During the first phase of Operation Steel Curtain, troops focused on Husayba, a town thought to have been used by insurgents as a base -- and a conduit into and out of Syria. Major sweeps there ended Monday.Marines entered Karabila early Thursday afternoon, discovering and detonating a car bomb and a warehouse that had been wired to explode. (Full story)Operation Spear also pushed through Karabila in June. But the U.S. military says that the latest operation will be followed by placement of a permanent Iraqi Army presence in Karabila, as was done in Husayba.Rice visitsU.S. Secretary of State Condoleezza Rice made surprise visits to the northern Iraqi city of Mosul and the capital, Baghdad, during a tour of the Middle East to promote democracy.After arriving in Mosul early Friday from Bahrain, Rice appealed for Iraqis to bridge their sectarian differences before the elections on December 15. (Watch: A wish and a warning from Rice -- 2:06)"The United States is not going to support any particular political candidate," news agencies quoted Rice as telling reporters traveling with her. "I want to talk about the importance of reaching across the sectarian divide, and the future of Iraq has to be one which includes everyone," she was quoted as saying. Rice said she delivered the same message of unity to Iraqi Deputy Prime Minister Ahmad Chalabi during their meeting in Washington this week. The once-dominant Sunni Arab minority boycotted U.S.-backed attempts to establish a representative government in Iraq and last month voted against a national constitution. America's top diplomat began her Iraq visit by meeting with political leaders in the majority-Sunni city of Mosul, including the U.S. ambassador to Baghdad, Zalmay Khalilzad. In her second visit to Iraq as secretary of state, Rice then traveled to Baghdad for meetings with Iraqi and U.S. military leaders as well as embassy officials. Rice arrived in Iraq the day after a series of attacks in the Iraqi capital on police and civilians, including a suicide bombing at a restaurant that killed at least 34 people, Iraqi police said. (Full story)Other developmentsPresident Bush on Friday accused critics of the Iraq war of distorting the events that led to the U.S.-led invasion in 2003, saying Democrats viewed the same intelligence and came to similar conclusions. Democrats responded immediately -- and angrily -- to Bush's comments. (Full story)Two U.S. soldiers were killed Friday and two others were injured in a vehicular accident during a combat logistical patrol northwest of Kirkuk. Two other U.S. soldiers died Thursday from small arms fire near al-Khalidiya, the military said Friday. The deaths bring the number of U.S. service members killed in Iraq to 2,065. Gunmen in two vehicles opened fire on a police checkpoint in central Baquba Friday, killing three police officers and wounding two others, police said. It happened around 6:30 a.m. (10:30 p.m. ET), near the Shareef Bridge. A spokesman for the Army's 3rd Infantry Division, 3rd Brigade said suspects had been detained and were being questioned. The bodies of two unidentified civilians were found in separate locations Friday in Baghdad. Both had their hands tied behind their backs and were blindfolded. They had been shot in the head execution-style, Baghdad emergency police said. A remotely detonated car bomb targeting an Iraqi police patrol in the eastern Baghdad neighborhood of Karrada wounded two police officers and a civilian, police said.CNN's Enes Dulami and Octavia Nasr contributed to this report.