The M16 assault rifle – mainstay of American Marines and many other forces since the 1960s – was discovered with a quantity of ammunition in a house in Carlton View, Little London.

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Three people – including the 15-year-old – were arrested when police from a specialist firearms unit swooped on the address at midday on Monday after a tip-off from a member of the public.

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The weapon had been dismantled into a number of parts and was found hidden in various locations within the house. Bullets were also discovered – it is not clear whether they fit the rifle.

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A man and a woman were arrested on suspicion of possession of an illegal firearm. The teenager was later released on bail, but the two adults were still in custody last night.

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Detective Chief Inspector Andy Williams, from the North West Leeds Police Division, said: "Weapons like this have only one deadly purpose and this significant seizure should serve as a demonstration of the hard work we undertake to combat gun crime across Leeds and West Yorkshire. Recovering weapons of this nature is very rare and I would like to reassure people that tackling gun crime remains a very high priority for us."

Anyone who suspects an individual of using or being in possession of an illegal firearm should contact police on: 0845 60 60 606 or Crimestoppers in confidence on: 0800 555 111.