Police are hunting two men riding off-road bikes after a vulnerable teenager was subjected to a knifepoint robbery.

The 17-year-old victim was forced to hand over his mobile phone after he was threatened by the two bikers.

The teenager was confronted by the two men after he stopped for a rest at Flappit Springs, in Halifax Road, near Cullingworth, as he walked back to his home in Keighley.

He was unhurt, but very upset by the incident, which happened at about 3.50pm on Friday.

The first suspect, who threatened the victim with a three-inch-long kitchen knife, is described as white, about 6ft-6ft 4ins tall, aged 18-20, and wearing white Nike trainers, dark tracksuit bottoms and a grey hooded top with a small Nike tick logo. His motorcycle helmet was a black off-road style with a chin guard visor with a picture of a white skull on the back. He was riding a large, yellow Yamaha off-road bike with a cracked rear mud guard and no number plate.

The second suspect is white, chubby to fat, and aged about 17. He was wearing a black hooded top, grey tracksuit bottoms and camouflage-coloured Converse footwear. He wore a black off-road style helmet with a distinctive red tribal pattern on the left side. He rode a new red Yamaha off-road bike.

Anyone with information should contact Detective Constable Paul Maxwell, at Keighley CID, via 101, or Crimestoppers, anonymously, on 0800 555 111.