Afghanistan on Thursday launched an investigation into whether the army was responsible for mortars fired into a wedding party that killed at least 20 guests in the restive southern province of Helmand.
Many of the dead were women and children and at least 50 people were injured in the incident late Wednesday in Sangin district, a Taliban stronghold where US and British troops were involved in years of fierce fighting.
The attack came during clashes in the area between Afghan forces and insurgents following the end of NATO's combat operations on December 31 after 13 years of war.
"We confirm the attack on a wedding ceremony in Sangin last night," deputy defence ministry spokesman Dawlat Waziri told AFP.
"We have appointed a delegation to do their investigation. They went to the area where the attack took place. After their investigation, we will share its results."
Karem Atal, head of the Helmand provincial council, said the Afghan army was to blame for the mistaken attack.
The Taliban issued a statement also saying the Afghan army was responsible.
"Last night, puppet security forces fired mortars from so many directions on a wedding ceremony," the statement said.
"In this attack, 62 people were killed including women and children, and many others wounded. We condemn this brutal and cowardly attack."
- Afghan army in charge -
President Ashraf Ghani said in a speech on Thursday that Afghan forces were now solely responsible for security, as the country struggles with a worsening insurgency.
"Today our security forces have become successful in defending sovereignty and taking full security responsibility," Ghani, who made no mention of the wedding deaths, said.
"In the past 13 years, due to the problems in the region and the world, this security was a joint responsibility. Now it belongs only to Afghans. But we are not alone, we have our allies, we will continue to work together."
The Taliban has claimed victory with the end of NATO's combat mission, adding that no peace talks could happen before all foreign troops leave the country.
The United Nations said civilian casualties hit a new high last year in Afghanistan with about 10,000 non-combatants killed or wounded -- 75 percent of them by the Taliban.
The end of NATO's mission brought "the longest war in American history... to a responsible conclusion", US President Barack Obama said this week.
About 17,000 foreign soldiers, most of them from the US, will still be deployed in Afghanistan.
Ghani paid tribute to the NATO effort, in contrast to his predecessor Hamid Karzai, who had a rocky relationship with the US-led military alliance.
"You have stood with us in tough circumstances, shoulder to shoulder," he told NATO commander General John Campbell, who attended the event at the presidential palace in Kabul.
"You have invested in our security forces and you have jointly completed the transition process."
Afghan officials and senior US officers have been pushing Obama to extend US involvement.
US troop numbers are set to halve within 12 months and fall to almost nothing in two years.