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 Baqubah 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 Baqubah, 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.

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.

U.S. military officials said Tuesday's attack does 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 of the 2nd Stryker Cavalry Regiment.

The Saad camp lies in an area with a large Shiite population on the eastern outskirts of Baqubah. Sunni militants have often targeted Shiites with suicide bombings.

The bombing occurred in a field outside the entrance to the joint U.S.-Iraqi base, where recruits were signing up.

Witnesses said an initial explosion about 8 a.m. drew a crowd that tried to evacuate victims. A second bomber then detonated his explosive vest among the rescuers.

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 Shiite-Sunni slaughter in 2006.

Last year, U.S. troops largely subdued militancy in Baqubah, which had been held by al-Qaida in Iraq and other Sunni extremist groups. But many insurgents were thought to have melted away and now appear to be regrouping.