A teenage boy was left terrified after two youths dragged him into a side street and threatened him with a makeshift weapon before making off with his mobile phone.
One of the youths grabbed his victim and pushed him away from the main road to an alleyway where his balaclava-clad accomplice was waiting - armed with a plank of wood with a nail sticking out of the end.
The 15-year-old's ordeal started as the first youth approached him on Bondgate, Darlington, at 7.20pm on Wednesday.
He was pushed into Four Riggs, where the armed thug dragged him into a corner and threatened to assault him with the plank, demanding: "Give me what you've got."
Detective Sergeant Alec Francis, of Darlington police, said: "He handed over the property because he was afraid of what was going to happen to him.
"It is a disturbing attack, there is no two ways about it - it's something which we've never come across for an awful long time.
"Fortunately, there were no injuries aggravating this incident further."
The black balaclava-clad youth was aged 15 to 18 years, white, 5ft 6ins tall, of athletic build and wearing a navy blue jacket with a zip up the front, jeans and black leather gloves.
His accomplice was of a similar age, of athletic build, 5ft 4ins to 5ft 5ins tall, with dark brown or blond hair which was short and flat. He wore a black "designer-type" jacket and light blue jeans.
"Whether it is somebody picking up on the current trend of theft of mobile phones, we are not sure, but they are good descriptions and we will be looking at the closed circuit television coverage in the area at the relevant time and hoping that will give us some leads to identify the people responsible," said Det Sgt Francis.
The Government has signalled a crackdown on mobile phone crime.
Only last week a mugger who attacked a teenager for his mobile phone was jailed by a court in London.
BT Cellnet is to introduce a new computer system to block calls from stolen handsets, while Vodafone is bringing in a six point anti-theft plan.
* Anybody who has any information is urged to contact Darlington police on (01325) 467681 or Crimestoppers on 0800 555111.
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