A soldier killed while on patrol in Afghanistan was a brave, beautiful and determined woman, her heartbroken sister has said.

Corporal Channing Day, who served with the 3 Medical Regiment, died alongside Corporal David O'Connor, of 40 Commando, after being injured on patrol with C Company in the Nahr-e Saraj district of Helmand province on Wednesday.

Lauren Day said there were no words to describe the deepest sadness felt by her family in Comber, County Down.

"Channing loved the army, if there was one thing she knew growing up, it was that she wanted to be a soldier, proven by the way she would march around the living room and never missed cadets," said Ms Day.

"She loved what she did and we are so proud of her. Channing grew up into the bravest, beautiful, determined woman. She has done more in her 25 years than most women her age and we are so very proud of everything she has achieved."

Cpl Day grew up in Newtownards before joining the Army in 2005. Ms Day said her younger sister was a shy child, but could later light a room.

She continued: "Channing being the amazing down to earth person she was, didn't realise how beautiful she was inside and out. She was the most caring, special and supportive sister and daughter always there for us when she was needed. We are an extremely close family and this has hit us all hard."

An initial review into the deaths of the British troops has revealed the killings were not caused by "friendly fire". The Ministry of Defence said an Afghan man, who is believed to have been a member of the Afghan Uniformed Police but who was not wearing uniform at the time, also died during the incident.

On Friday, Defence Secretary Philip Hammond paid tribute to Cpl O'Connor and Cpl Day and said what happened remains unclear.

He said: "It is a terrible tragedy in Afghanistan and I would like to send my heartfelt condolences to the family and friends of the soldier and marine who were killed. The circumstances are not entirely clear, there is an investigation ongoing. We know there were three people dead, one of them wearing civilian clothes. It is not absolutely clear as yet exactly what did happen and that investigation will continue until we find out exactly what happened."