The mountain road covers open countryside, moor land and hills

The victims were named by Dyfed-Powys Police as Danielle Caswell and Katie Roberts, both 15, and Louise Jones and Kayleigh Parry, who were 16.

They died when a Vauxhall Corsa crashed and rolled on the B4560 Llangynidr to Beaufort Road at 2120 GMT on Thursday.

The driver and front seat passenger, both 17, are both in hospital.

At a news conference on Friday, police revealed the two survivors have not yet been formally told by police about their four friends' deaths.

They are still to be interviewed by officers as they are undergoing treatment at Nevill Hall Hospital in Abergavenny. Their injuries are not said to be life-threatening.

'Not icy'

Superintendent Dean Richards said the families of the four dead teenagers were "devastated".

All six youngsters in the car were pupils at Glyncoed Comprehensive School in Ebbw Vale.

Supt Richards said the car - a black Vauxhall Corsa - had travelled around 70 feet on the opposite side of the road when it crashed.

It is not known where the youngsters had been or where they were heading to, but they were travelling back in the direction of the Ebbw Vale area.

Road conditions at the time were described as cold and frosty, but the roads were dry and not icy, said Mr Richards.

Danielle Caswell was travelling in the back seat of the car

He added: "There have been accidents on that particular stretch of road but I wouldn't call it a cluster stretch."

The car has been examined at the scene and police investigations will continue over the weekend.

The site of the accident was in the Dyfed-Powys police force area right on the border with Gwent Police. Both forces are working closely together.

Roger Williams, Liberal Democrat MP for Brecon and Radnorshire described the stretch of road as "difficult" and "exposed".

He said it crossed an open common and there were often animals near the roadside.

"It's one of those roads that, if we do get some severe weather, it is closed early on," he said.

"With winter coming suddenly this year, perhaps people weren't ready for the difficult conditions."

Police are appealing for anyone in the area at the time to contact them on on 0845 330 2000.