A bomb exploded Wednesday on a central Baghdad street, killing three boys and a girl as they were walking to school, police and relatives said. The dead included two brothers and their sister.

At least 14 other people, including six policemen, died in car bombings and shootings across the Iraqi capital.

The children were killed when a bomb exploded in central Baghdad's bustling Fadel area near a camera shop which also sold alcohol, police Lt. Ali Mittab said. The target was unclear but religious extremists often attack stories that sell alcohol or DVDs deemed pornographic.

Police said the children were aged from 10 years to 14 and included two sons and a daughter of Jamil Mohammed, a poor vendor who works in a nearby public market.

"We are poor people who has nothing to do with politics," the father sobbed at the local police station. "We only wanted to live a decent life. What is the guilt of my dead children? They were only heading to school. Now I am left with only two children. This is a disaster for my family."

At least three car bombs exploded across the capital on Wednesday, targeting police but killing and injuring ordinary Iraqis as well.

A parked car bomb exploded as police patrol passed, killing four policemen and wounding two civilians in northern Baghdad, said Lt. Nadhim Nasser.

Another car bomb blast killed two civilians near Baghdad's University of Technology, according to Jabir Mohammed of the eastern Baghdad emergency services department. Five people were wounded, three of them police, he said.

A third explosives-rigged vehicle blew up near a gas station as an Iraqi police patrol passed in downtown Baghdad's Karradah area, wounding five policemen and three civilians, said Maj. Abbas Mohammed.

Gunmen firing from two cars shot and killed police Capt. Hussein Ali Youssef and his driver, also a policeman, in southwestern Baghdad's Sadiyah neighborhood, said police Lt. Aqil Fadil.

Police said they found the bodies of five men Wednesday shot in the head and dumped near a Shiite neighborhood of western Baghdad. Their identities were unknown but they appeared to be the victims of sectarian tit-for-tat killings which have swept the capital for months.

Another civilian was slain in a drive-by shooting about noon in western Baghdad's Ghazaliyah district, police said.

Iraqi authorities, meanwhile, have declared a bird flu alert in the southern province of Maysan and called for security forces to prevent people from carrying birds in and out of the area, health officials said Wednesday.

The alert is the latest measure taken by Iraqi health authorities to combat the deadly H5N1 bird flu strain following last month's discovery of the country's only confirmed case of the disease in a human.

Minister Abdel Mutalib Mohammed declared the alert after birds suspected of having the disease were discovered in Maysan, a major southern trade route in Iraq, said Dr. Ibtisam Aziz Ali, spokeswoman for a government committee on bird flu.

Mohammed said the government has to "totally close" Maysan using Iraqi soldiers and police and carry out culling of poultry. He held talks late Tuesday with local health authorities and tribal sheiks in Amarah, 180 miles southeast of Baghdad, to brief them on the bird flu threat and government measures to combat it.

"The disease has apparently spread among local birds, not migratory birds," Mohammed said. "I have seen five centers where infections have been detected by rapid laboratory testing. Now we have declared a state of health alert."

Maysan includes some of Iraq's famous marshlands, and U.S. and U.N. officials fear the deadly disease could spread rapidly if it reaches the area rich in bird life.

Bird flu has killed at least 91 people since 2003, according to the World Health Organization. Almost all the human deaths have been linked to contact with infected poultry, but experts fear the H5N1 virus could mutate into a form that spreads easily among people, possibly sparking a pandemic.

Tests are being carried out at a WHO-approved lab in Egypt on samples taken from about 10 suspect human cases in Iraq, including the dead uncle of a girl who died Jan. 17 of the disease in Iraq's northern Kurdistan region.

Among the samples are those taken from an Amarah man who owned birds and died earlier this month. Five of his relatives were also hospitalized with flu-like symptoms, but Iraqi officials have said since they do not suspect they had H5N1.