British troops are based in Helmand province, southern Afghanistan
Four Afghan civilians have been killed in an airstrike by British forces, the Ministry of Defence said.
The attack happened when troops called for help during a Taleban ambush in Helmand province, south Afghanistan.
"We deeply regret that this incident happened and do everything we can to mitigate this from happening," the Ministry of Defence (MoD) said.
The four bodies - two women and two children - and one injured person were found when troops inspected the area.
The MoD said in a statement: "We can confirm UK forces were involved in an operation in the south of Helmand Province.
"This incident is currently under investigation and it would be inappropriate for us to comment."
The British troops had been caught up in an intense fire fight after being ambushed, the MoD spokeswoman said.
The civilians were unintentionally killed after air support was called in and directed on to the area where the Taleban appeared to have been operating, the MoD said.
An injured person was evacuated to the British field hospital at Camp Bastion for medical treatment.
Nato spokesman Brigadier General Carlos Branco revealed details of the incident at a news conference in Afghanistan.
He spoke only of the Nato-led International Security Assistance Force's role, and later the MoD confirmed UK troops had been present.
The MoD did not say if the aircraft was British.
Brig Gen Branco said: "During the ensuing fight, two women and two children, part of a group of civilians who were in the vicinity of the action, were killed.
"We deeply regret the loss of innocent life and injuries and we are saddened that casualties were caused as a result of a deliberate attack against Isaf forces instigated by insurgents."
Prince Harry worked with the air support, the British Forward Air Controllers, until he returned from Afghanistan less than two weeks ago.