By Khaled Farhan

NAJAF, Iraq, Feb 2 (Reuters) - Three teenage Iraqi brothers thought they had found a good way to make money for their impoverished family -- buying and selling birds.

But as they bought their first birds at a popular pet market in southern Baghdad on Friday, an explosives belt strapped to a female bomber blew up. Kareem, 15, and Sajjad, 14, were killed instantly, said their uncle Mohammed Hussein Obeid.

Akram, 17, struggled home with severe injuries to tell his family, but died later in hospital.

The brothers were among 99 people killed in twin blasts on Friday that the U.S. military blamed on al Qaeda in Iraq, saying there was some evidence that the bombers had been mentally handicapped.

The teenagers' family gathered on Saturday to bury them in a simple funeral in the Shi'ite holy city of Najaf, south of Baghdad, whose cemetery is an important burial ground for Iraqi Shi'ites.

"They had one mobile phone and decided to sell it to use the money to trade in birds," Obeid said. "They only decided to start this simple project yesterday."

The attacks were a stark illustration of how violence still haunts Baghdad, where a sharp drop in attacks in recent months had led many Iraqis to hope that their country might be starting to return to some sense of normality.

The bomber at the southern Baghdad market killed 37 people including the brothers. Another woman killed 62 people at the Ghazil pet market in central Baghdad.

"Kareem and Sajjad died instantly. Their bodies were totally charred from the explosion," said Obeid.

"Akram rushed to the family to say his brothers had been killed. He was taken to hospital, where he died. The doctors said he was too badly wounded in the liver."

The boys' mother, covered by a traditional black abaya robe, wailed as three wooden coffins containing her only sons were lowered into dirt graves.

Her face was bruised from beating herself with her hands. She threw dirt on her head, an Iraqi tradition that shows she has lost someone very dear to her.

"After you, who will take care of us and bring us food? Who will bring us juice to drink?" she screamed.

The boys' father lay at their home in Baghdad, paralysed from a chronic illness.

Obeid stood at the edge of the graves and wept. "Don't be afraid, don't be lonely," he told Akram, Kareem and Sajjad.

"Your father will follow you soon. He is very sick, and the shock of this will be too much for him." (Writing by Dean Yates; Editing by Kevin Liffey)

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