BAGHDAD, Iraq - Insurgents killed at least 20 people in three separate attacks targeting Iraqi security forces in Baghdad today, including one by a man who set off hidden explosives while waiting in line outside an army recruitment center, police said.

A similar attack Wednesday by a suicide bomber standing in a line outside a police recruitment center in the northern Kurdish city of Irbil killed 60 and wounded 150.

The attacks are part of an escalation of violence aimed at destabilizing Iraq's new democratic government. The insurgents often target Iraqi security forces, which are being recruited and trained by the U.S.-led coalition as part of its eventual exit strategy.

In the deadliest attack today, a man carrying hidden explosives set them off while standing in a long line of job applicants outside an Iraqi army recruitment office in central Baghdad, killing at least 11 people, police and hospital officials said. At least six people were wounded in the 8 a.m. attack, a police officer said on condition of anonymity.

The recruitment center, which has been hit by insurgent attacks before, is surrounded by a cement wall topped with barbed wire. It is located on the site of a former Iraqi army airfield.

"While we were standing in a line, a man walked past, right up to the heavily guarded entrance gate, as if he wanted to ask the guards a question," said Anwar Wasfi, who was standing toward the end of the line of recruits.

"Suddenly, an explosion occurred, and I was knocked over," Wasfi said during an interview at Yarmuq Hospital, where he was being treated for leg and arm wounds.

The U.S. military said it could not immediately confirm the attack, which was reported to be less than a half mile from the Green Zone, where Iraq's parliament and embassies are located and heavily protected by American forces.

In western Baghdad today, insurgents attacked two police patrols, killing a total of nine policemen, an official said.

Gunmen opened fire on a patrol in the Al-Amil area of western Baghdad at 6:45 a.m., killing eight policemen and wounding two, said police Maj. Mousa Abdul Karim.

About 15 minutes after the Al-Amil attack, a suicide car bomb exploded in the nearby Al-Gazaliya area, killing one policeman, wounding six and destroying four of their cars, said Karim.

The U.S. military said it had no immediate information about attacks in Al-Amil or Al-Gazaliya.

Wednesday's brutal attack in Irbil, 215 miles north of Baghdad, was the deadliest one in Iraq since Feb. 28, when a suicide car bomber struck a crowd of police and national guard recruits in Hillah, south of Iraq's capital, killing 125 and wounding more than 140.

The Irbil tragedy left pieces of flesh spattered on the walls outside the police recruitment center. Nails and shards of metal were packed in with the explosives to maximize casualties.

A Sunni militant group, Ansar al-Sunnah Army, claimed responsibility, saying the attack was revenge for Kurdish cooperation with U.S. forces.