Kabul, Afghanistan ? An Afghan toddler taken to the United States for surgery to fix a life-threatening heart ailment died Friday, two days after returning home to a muddy refugee camp from the trip arranged with the help of U.S. soldiers.

Army medical officers said 16-month-old Qudratullah Wardak’s repaired heart had likely given out as his father tried to comfort him in the family’s drafty tent near an American base outside the Afghan capital. The cause of death could not be determined because the Afghan tradition of quickly burying the dead made an autopsy impossible.

The boy had been treated at a children’s hospital in Indianapolis after Indiana National Guard soldiers and the Rotary Club learned of his condition and the family’s inability to find care in Afghanistan, which has one of the highest infant mortality rates in the world.

“This is a very sad day,” said Maj. Eric Bloom, a U.S. military spokesman in Kabul. “So many people, literally from around the world, came together to help this young Afghan boy.”

On Wednesday, U.S. troops had escorted the boy and his father home to a joyous welcome at the camp next to an Afghan military barracks. More than 100 adults and children turned out to greet them in a heavy downpour, applauding wildly when the boy’s father, Hakim Gul, emerged from a pickup truck clutching his son, who looked plump and healthy after the two-day journey home.

Bloom said the boy’s uncle arrived before dawn Friday at the U.S. military’s Camp Phoenix with news of the child’s death. Army medical officers sent to the camp found the child lying under a blanket on a bed placed in front of the family tent, his veiled mother weeping over him.

“He still had glitter in his hair, from the big party they had for him,” Capt. Michael Roscoe said later at Camp Phoenix, headquarters of the U.S. training program for the new Afghan army.

Without an autopsy and no outward sign of what killed the child, “our best guess is that it was something to do with his heart,” Roscoe said.

Another uncle, Abdul Malik, said the boy seemed well on Thursday evening after receiving a dose of medicine prescribed by the doctors in Indianapolis. But the boy developed problems about 3 a.m., and his parents woke the rest of the family in a panic.

Hakim Gul Wardak holds his son Qudratullah Wardak after a news conference Wednesday at a U.S. base near Kabul, Afghanistan. The Afghan toddler -- sent to Indianapolis for surgery to fix a life-threatening heart condition -- died in his father's arms Friday, two days after his joyful return home.

“His father and mother were putting their hands over his heart and said it was beating very fast,” Malik said at the family’s tent. “They gave him his medicine for pain, and he seemed to calm down. His father felt for his heart again, then he asked me to try, but the heartbeat was gone. Everybody was crying.”

Malik said the boy’s parents and grandfather had departed for their home province of Kunduz, 150 miles to the north, to bury him.

Two cardiologists who helped care for Qudrat during his stay at Riley Hospital for Children in Indianapolis refused to speculate on why he might have died so soon after returning home to Afghanistan.

Dr. Richard Darragh said there were no signs of complications when the child was released and cleared to travel.

Darragh said the list of potential complications following complex heart surgery such as that undergone by Qudrat could fill a medical textbook, he said, and some might not occur until years later.

The boy’s long journey began in September, when an Indiana National Guard doctor examined him at the camp and discovered a heart defect. Doctors in Indianapolis later found that his heart’s main blood vessels were reversed, a condition that stunted the baby’s growth.

He weighed about as much as a typical 5-month-old when he arrived in late February in the United States.