Scattered sandals and overturned bicycles were all that remained hours after suicide bombers struck the Saad military camp. Medical staff had finished unloading the white body bags at the nearby hospital, where the wounded moaned on bloodstained floors and weeping soldiers kneeled over slain comrades. The twin blasts in Baqouba recalled the scenes of mass terror and grief that were almost a daily routine before last year's steep decline in violence. In an old tactic of Sunni extremists, two suicide bombers set off explosives among the army recruits Tuesday, killing at least 28. Violence also flared in the northern city of Mosul, where a dozen people died in bombings that targeted the Iraqi police and army. The attack in Baqouba, capital of Diyala province, came ahead of a planned Iraqi military offensive to halt attempts by militants to regroup in the volatile area northeast of Baghdad. Late Tuesday, the US military said an American soldier was killed by a bomb while searching a house in the province Tuesday, but gave no other details. Diyala is critical to Baghdad's security because of its strategic importance as an entrance to the capital and a threat to supply routes going north. The ethnically mixed area also borders Iran, which the United States has accused of helping militants to stage attacks on American troops. US military officials said Tuesday's attack did not reflect any increase in militant strength in the area. "I don't think this changes the security situation. It's just an isolated incident. This is the way al-Qaida grabs attention," said Maj. Jay Gentile, with the 2nd Stryker Cavalry Regiment. The Saad camp lies in an area with a large Shi'ite population on the eastern outskirts of Baqouba. Sunni militants have often targeted Shi'ites with suicide bombings. The bombing occurred in a field outside the entrance to the joint US-Iraqi base, where recruits were signing up. Witnesses said an initial explosion at about 8 a.m. drew a crowd that tried to evacuate victims. A second bomber then detonated his explosive vest among the rescuers. "I lifted one of the wounded, and while I was carrying him away from the site, another explosion took place. I got hurt and the injured man suffered more injuries," said a man who did not want to be named because of safety concerns. A few hours after the bombing, the site had been cleared, but a large area of grass was scorched from the blast. More than a dozen pairs of sandals lay scattered, evidence of the Iraqi casualties. A dozen bicycles lay on the ground. The explosions killed 28 people and wounded at least 57 recruits, a police official said. He spoke on condition of anonymity because he was not authorized to speak to the media. An Iraqi military officer in Baqouba, 35 miles from Baghdad, said soldiers were among the casualties. He also spoke on condition of anonymity for the same reason. It was the bloodiest attack in Iraq since June 17, when a truck bombing killed 63 people in Hurriyah, a Baghdad neighborhood that saw some of the worst Shi'ite-Sunni slaughter in 2006. Last year, US troops largely subdued militancy in Baqouba, which had been held by al-Qaida in Iraq and other Sunni extremist groups. But many insurgents were believed to have melted away and now appear to be regrouping. Iraq's Interior Ministry spokesman, Maj. Gen. Abdul-Karim Khalaf, said Sunday that the government's planned operation in Diyala would be "the last surge." Al-Mada, an Iraqi newspaper, on Tuesday reported Khalaf as saying that the file on the Diyala operation had been handed to Prime Minister Nouri al-Maliki, who will decide when to launch it. The US military says it will support the effort, which it called an enhancement of existing patrols and actions there. Loyalists of Saddam Hussein's regime had homes in Buhriz, a southern suburb of Baqouba, and the area served as a staging ground for Sunni attacks that drove Shi'ites out of the city. Abu Musab al-Zarqawi, leader of al-Qaida in Iraq, was killed by a US airstrike in Diyala province in June 2006. On June 22, a female suicide bomber concealing explosives beneath her black robe struck outside a government complex in Baqouba. At least 15 people were killed and more than 40 were wounded. A car bomb across the street from the same compound killed at least 40 people in April. The road on the outskirts of Baqouba winds past concrete houses, many of which are heavily pockmarked with gunfire. Some have ceilings or roofs caved in from heavy fighting or bombing. But there are signs that the city is coming back to life. Shops are open and a smattering of pedestrians stroll along the streets. So far this month at least 58 people have been killed in Diyala - far lower than the 224 deaths in July 2007, according to figures compiled by The Associated Press. Last month saw at least 36 killings in Diyala - down from 213 the previous June. The decline in violence in Iraq has been driven by a variety of factors, including the 2007 US troop surge and a Sunni revolt against al-Qaida in Iraq. US-backed Iraqi forces have scored successes in offensives against Shi'ite militants in Baghdad's Sadr City district and the southern cities of Basra and Amarah, and against Sunni extremists in Mosul in Nineveh province. Baghdad, Nineveh and Diyala are the three deadliest provinces in Iraq, though Diyala is far less populous than the two others. In western Mosul on Tuesday, a bomb near an Iraqi police station killed four Iraqi civilians, the US military said. Half an hour later, one Iraqi police officer and seven civilians died in a suicide car bombing in the east of the city, the military said. Three other bombs in Mosul wounded 15 people, including 11 police and soldiers, Iraqi authorities. Also Tuesday, the US military said it had captured the Iranian-trained leader of an explosives cell in the Azamiyah district of Baghdad. It said the suspect has been linked to attacks against US and Iraqi bases in the capital.