A man was threatened with what he thought was a gun as he sat in his car at a set of traffic lights in Hove.
He was forced to hand over cash and his watch in the early hours of Saturday.
The victim, who has not been named, stopped at the junction of Portland Road and Sackville Road at 12.37am.
The occupants of the car behind, a burgundy Peugeot, got out and threatened the victim with the gun and punched him in the head before robbing him.
Two of the men were black and the third was white.
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