A senior regional official says Afghan soldiers were to blame for a mortar strike that killed at least 27 people at a wedding in southern Helmand Province.
Among those killed by mortar rounds on December 31 were women and children, and more than 50 people were wounded.
The injured have been taken to the main hospital in the provincial capital, Lashkar Gah.
Mohammad Jan Rasoulyar, deputy governor of Helmand, said troops "fired mortar rounds on a wedding ceremony after militants in the same area attacked an army checkpoint."
Speaking to the French AFP news agency on January 2, he said the Afghan Army troops accused of firing the rounds "have been referred to a military court."
Four soldiers, including one commander, were arrested and taken to Lashkar Gah.
Omar Zwak, spokesman for Helmand's governor, told RFE/RL's Radio Free Afghanistan on January 2 that those accused in the attack were in custody.
He said: "They are now in the central military base, in the provincial capital, and they are under an investigation."
Dozens of people demonstrated on January 1 over the bloodbath.
It occurred on the eve of a military ceremony in Kabul at which President Ashraf Ghani congratulated the Afghan Army and police for taking over from NATO forces, who ended their combat mission at the end of the year.
Hashem Alekozai, a member of the upper house of the Afghan parliament, said the provincial governor must resign in the wake of the attack.
He said: "The administration in Helmand is very weak. It cannot bring security to us and the security forces are inflicting misery upon our people and cannot bring to justice those who are behind the killing of our people."
Alekozai added: "[The office of the governor of Helmand] has failed in fulfilling its duty. In order to show respect to the president and the people of Helmand, the governor must resign from his position."
Dozens of people have continued to stage protests around the province over the incident, calling on the government for justice.
With reporting by AFP