Afghan officials say six Taliban prisoners on death row were hanged on May 8 in the first set of executions endorsed by President Ashraf Ghani since he took office in 2014.
Local media reported that the executions were carried out in Kabul's Pol-e Charkhi prison.
The presidential palace said in a statement that "in accordance with the Afghan constitution...Ghani approved the execution of six terrorists who perpetrated grave crimes against civilians and public security."
The statement said the executions were conducted after a fair legal process and in accordance with the country’s constitution and Islamic laws.
"This order has been carried out today after...considering the human rights obligations of Afghanistan...and in accordance with Afghan laws," the statement said.
Ghani has toughened his stance against the militants after a major Taliban assault on Kabul that killed 64 people and wounded another 340 last month.
Ghani vowed a tough military response against the Taliban and pledged to enforce legal punishments, including executions of convicted militants.
Afghanistan's National Directorate for Security gave the identities of the six condemned men while detailing attacks for which they were convicted.
The Taliban said in a statement that the executions will not "deter them from their goal, as the fight for over the past 10 years has proven."
Even before the hangings, the militant group had warned of "serious repercussions" if Ghani would approve the death sentences.
The group has been waging an insurgency against the Afghan government since 2001 when it was ousted from power by U.S.-led forces.
The United Nations expressed regret over the executions of the six men in a statement issued to the press.
“The United Nations notes that there is no conclusive evidence of the deterrent value of the death penalty and that the use of capital punishment does not contribute to public safety,” the May 8 statement by the UN Assistance Mission in Afghanistan (UNAMA) said.
"UNAMA encourages the Government of Afghanistan to expedite legal reform, which would allow death sentences to be commuted to life imprisonment," the statement added.
Amnesty International had urged Ghani not to sign the execution orders.
“By hastily seeking retribution for the horrific bombings that killed over 64 people in Kabul last month, the government of Afghanistan’s plans to execute those convicted of terror offences will neither bring the victims the justice they deserve, nor Afghanistan the security it needs,” the rights watchdog said on May 4.