Claims that "rogue" Special Air Service (SAS) soldiers killed unarmed Afghan civilians in cold blood and attempted to cover up the evidence should be probed in an independent inquiry, Jeremy Corbyn has said.
The Labour leader said there is a risk the British armed forces' reputation for decency and bravery will be undermined unless the claims in the Sunday Times are investigated.
According to the newspaper, which quoted senior military police and defence sources, there is "strong evidence" SAS personnel killed rather than captured unarmed Afghan civilians who were suspected of being Taliban insurgents during night raids on their homes.
The allegations emerged in Operation Northmoor, a Royal Military Police (RMP) investigation, the Sunday Times reported.
The Ministry of Defence (MoD) said the RMP found no evidence of criminal behaviour by British armed forces in Afghanistan to date.
In February, Defence Secretary Sir Michael Fallon announced 90% of the probe's misconduct cases involving British troops who served in Afghanistan were to be dropped, amid controversy over a discredited probe into Iraq war veterans.
Some 675 allegations of abuse were being looked at by Operation Northmoor and many of the cases came from law firm Leigh Day, which was also behind a number of claims in the dropped Iraq Historic Allegations Team (IHAT) investigation.
Commenting on the claims, Mr Corbyn said: "The allegations of unlawful killings and war crimes in Afghanistan are extremely serious and must be fully investigated.
"Our armed forces have a reputation for decency and bravery. If we do not act on such shocking allegations we risk undermining that reputation, our security at home and the safety of those serving in the armed forces abroad.
"Our values and respect for the rule of law require full accountability. We owe it to our armed forces and the victims and their families to ensure that a thorough investigation takes place.
"There can be no question of a cover up. The Government must now establish an independent inquiry into what has taken place."
An MoD spokesman said the RMP had full independence over the direction of Operation Northmoor.
He added: "The Royal Military Police has found no evidence of criminal behaviour by the armed forces in Afghanistan. They have discontinued over 90% of the 675 allegations made and less than 10 investigations remain.
"Our military served with great courage and professionalism and we proudly hold them to the highest standards. Where allegations are raised it is right they are investigated."