The killings came as president Ashraf Ghani marked the country’s transition to full sovereignty after the formal end of the 13-year international military mission.
The head of the army in southern Helmand province, where the incident happened, said investigations were focusing on whether the house had been deliberately targeted by soldiers in checkpoints at least 3km (1.8 miles) away.
General Sultan Mahmoud said early investigations indicated that artillery had been fired in the direction of the house from both the north and south from a distance of 3km.
He added: “We are seeing no evidence that the Taleban can fire from that distance, and, as the Taleban positions were only one kilometre from the checkpoint, why was it necessary to use artillery that can travel so far?”
The incident happened in volatile Sangin district while guests were awaiting the arrival of the bride at the home of her cousin, Abdul Haleem, in Sarwankhala district.
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The tribal leader of Sarwankhalain, Taj Mohammad, presented 35 bodies to provincial governor Mohammad Naeem, but deputy police chief Bacha Gull said he could confirm only that 28 people had been killed.
The strike, which took place late on Wednesday, also wounded at least 51 people, he said.
Abdullah Jan, 12, said he still did not know where his mother was after he was knocked unconscious while running to welcome the bride and woke up hours later in hospital.
“We were ready to go to sleep when my auntie came and said the bride had arrived. My mother went out to see the bride and I was running after her, toward the door, when I heard the sound of blast and some bright flash like a fire hit me,” Abdullah said. Both his legs were broken and he suffered burns to his stomach.
“Then I couldn’t see anything. I heard people shouting and after that I didn’t know what happened. The next time I opened my eyes, I was here,” he said.
Sangin, in the poppy-producing Helmand River valley, has been the scene of fighting between government forces and the Taleban for the past six months, since United States forces departed as part of the transition to Afghan sovereignty.
The international mission to rid Afghanistan of insurgents under the leadership of the US and Nato officially ended on Wednesday.
Afghanistan took full responsibility for its own affairs from yesterday.
Mr Ghani told Afghans to support their security forces in the interests of building a strong and peaceful Afghanistan.
He said: “If, a year ago today, you had listened to regional and international analysts, they would never have thought that today would happen. They were thinking how can a country with the problems that Afghanistan has successfully complete a security and political transition.”
He thanked the international community for the sacrifices soldiers had made during the Nato mission.
He added: “I hope it is clear that equipping, supporting and strengthening Afghan security forces is an investment, so that the citizens of your country can be safe.”
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