Haji Malim Toorylai, the Maruf district chief, said, “The man believed he was attacking the N.D.S. delegation; he probably was not aware of the foreign soldiers coming with them.” An official of the NATO-led International Security Assistance Force gave a similar assessment. “It was an N.D.S. attack on N.D.S., and we happened to be in the wrong place at the wrong time,” the official said.

The man who carried out the attack was named Abdul Wali and was from Zirak, a village in Maruf, said Mr. Toorylai. Maruf, the easternmost district in Kandahar Province, is sandwiched between Pakistan’s ungoverned tribal areas and Afghanistan’s Zabul province, a rural desert area where the Taliban have a strong presence.

The former American military officer who was killed was Dario Lorenzetti, a Fort Worth native, The Fort Worth Star-Telegram reported Sunday, describing him as a West Point graduate.

In a tragic coda to Saturday’s story, the suicide bomber’s 9-year-old brother was killed in revenge by the brother of one of the Afghan victims, said Shamsullah, a Maruf local, who commands a guardpost.

“The 9-year-old boy was killed in front of his mother and father,” said Shamsullah. “The parents didn’t know their son Abdul Wali was going to commit suicide.”

The separate case of three children allegedly killed in a coalition strike was reported by local officials in Helmand Province’s Nawa district. The officials said that the children were killed in a NATO strike on Sunday afternoon as they were gathering dung to burn as fuel, a common practice in the desert reaches of southern Afghanistan where there are few trees.

“When we reached the area I saw the three bodies of children, two boys and one girl, ages 8 to 12 years old. They were from the same family,” said Haji Hayatullah, a member of the tribal council in the Nawa district. Their family is in the livestock business and raises goats and sheep on government land, he said.