It called the killing of 27 passengers on a bus in southern Afghanistan on 16 October "a crime against humanity".
Gunmen associated with Taliban insurgents reportedly pulled 50 passengers off the bus on the Kandahar-Herat highway, beheading six and shooting dead 21 of them. Through their purported spokesmen, the insurgents dubbed those killed as "soldiers of the Afghan National Army and police".
However, the defence and interior ministries have denied the victims were working for them.
"The killing of these people - regardless of whether they were working for the government - is unjustifiable. It is a crime against humanity," Ahmad Nadir Nadiry, a spokesman for the AIHRC, told IRIN in Kabul.
Anthony Dworkin, executive director of Crimes of War - a Washington-based project overseeing the laws of war in conflicts around the world - said the identity of the victims will determine the legal characteristics of the incident.
"It is always a war crime for fighters to deliberately kill civilians, but the laws of war generally permit fighters to kill members of enemy forces unless they are wounded, surrendering or have been taken prisoner," Dworkin told IRIN.
"It would not be a war crime to kill soldiers, even if they were dressed in civilian clothes," he said.
According to Dworkin, crimes against humanity occur when attacks on civilians are "systematic and widespread" in nature.
The AIHRC said the insurgents had long adopted a policy of systematic attacks on civilians and have thus committed crimes against humanity.
The AIHRC said warring parties had repeatedly violated international humanitarian law, the Geneva Conventions and Afghan laws over the past few years.
Little has been done to prevent further violations and/or provide compensation for past violations, rights activists said.
Despite numerous cases of war crimes and crimes against humanity allegedly committed over the past three decades, no formal, independent investigation has been conducted which could identify perpetrators and victims.
Nadiry said the security situation had not been conducive to an independent international investigation into alleged cases and that the government had also been unsupportive of such efforts.
As a result there has been a lack of accountability among all parties. "There is a total state of impunity, particularly on the insurgents' side," said Nadiry, adding that the Taliban were brazenly disregarding all Afghan and international laws.
Civilians bearing brunt of conflict
Civilians have borne the brunt of the conflict.
At least 1,400 civilians died in insurgency-and-counterinsurgency-related violence from January to August, according to a report by the UN Secretary-General.
Many civilians have died as a result of "asymmetric" tactics such as the use of suicide attacks, landmines and improvised explosive devices.
Over 50 people, mostly civilians, died in a suicide blast in front of the Indian embassy in Kabul on 7 July.
The insurgents have also been accused of deliberate, indiscriminate and direct attacks on aid workers, teachers and other civilians.
Hundreds of non-combatants have also been killed by Afghan government and international forces, particularly during aerial strikes. Up to 90 civilians were killed when US forces bombed a village in Herat Province on 21 August, the UN Assistance Mission in Afghanistan said in a statement.