BAGHDAD (AP) -- A suicide bomber pushing an electric heater atop a cart packed with hidden explosives attacked a high school north of Baghdad on Tuesday, leaving students and teachers bloodied and bewildered as insurgents appeared to be expanding their list of targets.
The bombing -- one of two attacks near Iraqi schools on the same day -- follows a wave of recent blasts blamed on al-Qaida in Iraq against funerals and social gatherings.
The trend points to the possibility that al-Qaida has shifted tactics to focus increasingly on so-called soft targets and undermine public confidence that things are looking better in the country. The backlash also coincides with a U.S.-led offensive trying to uproot insurgents from strongholds around Baghdad.
In the suicide attack, the bomber posed as a shopper or merchant transporting an electric heater on a chilly winter day -- an apparent attempt to deflect attention from the explosive-rigged cart.
The blast struck the front of a two-story schoolhouse in Baqouba about 8:30 a.m., half an hour after classes began. Panicked parents rushed to find out if their children were alive or dead.
A 25-year-old male bystander was killed and 21 people were wounded -- 12 students, eight teachers and one policeman, according to a doctor at Baqouba General Hospital who spoke on condition of anonymity because he was afraid of being targeted by militants.
"I can't think of any reason to target students," said 15-year-old Mohammed Abbas, his wounded head in a bandage as his father stood near his hospital bed in Baqouba, about 35 miles northeast of Baghdad. "We did not expect that explosions would reach our school."
In the other attack, a roadside bomb exploded next to a girl's high school in Baghdad's western district of Amiriyah, wounding a 7-year-old boy who was passing by. But police said the target was an American patrol, not the school.
Insurgents appear to be looking for ways to bypass the heavy security cordons and patrols that cover any major event or site.
During last week's observances of Ashoura, the most important holiday in the Shiite calendar, there were no attacks on the main procession in the holy city of Karbala, where hundreds of thousands marched. Instead, militants struck with suicide bombings and rocket fire on small gatherings of worshippers north of Baghdad, killing dozens.
In an attack at a tribal gathering near Fallujah on Sunday, the bomber was a 15-year-old boy carrying a box of candy. Women, too, are being used more in suicide bombing -- four times in the past three months.
With the help of Iraqi troops and Awakening Councils -- mostly Sunni tribal groups that have turned against al-Qaida in Iraq -- the U.S. military says it has gained command of many key areas across central Iraq.
But it is far more difficult to prevent isolated suicide strikes against less-protected targets.
"There were no police or army inside my school," said Ahmed Alwan, the headmaster of the high school targeted in Baqouba. "I think that the goal of this attack was to destroy any sign of education and culture in this country."
Alwan said he was in his office when the attacker blew himself up at the outside gate, leaving a crater in the street.
"After the tremendous explosion, there was total darkness in my room," he recalled. "The false ceiling and the books on the shelves fell on me, and an object hit my head. I crawled outside the room, and people put me in the ambulance."
Abbas, the 15-year-old student, said he was walking outside his classroom after a test when he heard a big boom. "Immediately I fell down, and the next thing I was aware of was a doctor treating me in the hospital," he said.
The force of the blast shattered windows in the school, sending shards of glass across classrooms into exposed skin.
"What is our guilt that caused the terrorists to target us?" a teacher asked, crying as blood covered her face ripped by sharp bits of glass.
"I blame the government, which is unable to protect schools," said the teacher, who would identify herself only as Um Ibrahim. She said she could not find her son who attends the school.
The school bombing was not the only attack Tuesday in Diyala province, which has defied the nationwide trend toward lower violence over the past six months.
Three miles south of Baqouba, gunmen broke into a house and killed six men in a family for cooperating with the Iraqi army, an army official said. The men had given information on al-Qaida movements to local Awakening Council members, the official said.
The attack took place in al-Abara village, an al-Qaida stronghold until Awakening Council members chased out the militants a few months ago.
In other developments, the U.S. military said a soldier killed over the weekend south of Baghdad was the first American casualty in a roadside bomb attack on the newly introduced, heavily armored MRAP -- Mine-Resistant, Ambush-Protected vehicle.
In Baghdad, Iraq's parliament passed a law to change the Saddam Hussein-era flag, meeting the demands of Iraq's Kurdish minority, which threatened not to fly the banner during a pan-Arab meeting in the Kurdish-run north next month.
A U.S. soldier was killed and another was injured when their vehicle rolled over in the northern city of Kirkuk, the military announced. It said the cause of the accident was not related to combat and was under investigation.
At least 3,930 members of the U.S. military have died since the Iraq war started in March 2003, according to an Associated Press count.
Associated Press writer Sameer N. Yacoub contributed to this report.