A Hong Kong pawnshop which bought a 16-carat yellow diamond is fighting to keep the gem after a London jewellers claimed it was stolen from them in a raid five years ago, a report said Saturday. The diamond was reportedly snatched from ultra high-end jeweller Graff Diamonds in 2007 after two Bentley-driving robbers pretending to be shoppers raided the shop and got away with a haul worth $20 million. Its origin was discovered when Hong Kong's Yau On Pawn Shop sent it to a New York gem-grading laboratory for certification, according to the South China Morning Post, prompting a lawsuit from Graff seeking its return. Danny Hung, a director at the pawnshop, told the paper that Yau On paid HK$3 million (US$386,000) for the diamond in November 2010. He said it was bought from a private seller who he described only as a Chinese national and that the shop had documentation for the purchase. "We've followed all necessary procedures," he said, adding that the shop "will not give up" its legal battle for the ownership of the gem. Hung could not be immediately reached for comment by AFP. The diamond is now being held at the New York laboratory pending the lawsuit filed by Graff at a court in Manhattan. Hong Kong police regularly update pawnshops on property reported stolen in the city, according to the Post, but Hung said the list does not include items stolen overseas.