In a large bowl, whisk together the marinade ingredients. Add the chicken, mix well, then cover and marinate in the refrigerator for at least 2 hours, or preferably overnight.
Soak 12 wooden skewers in plenty of cold water for at least 30 minutes. Alternatively, use metal skewers. Preheat a grill to a moderate heat.
To make the dipping sauce, combine the ingredients in a small saucepan and heat gently, stirring frequently, until the sugar has dissolved. Simmer gently for 5 minutes, then remove from the heat and leave to cool.
Remove the chicken from the marinade and thread onto the skewers, reserving the marinade. Grill for 10 minutes, brushing the kebabs after 5 minutes with the leftover marinade mixture to keep the chicken moist. Turn the kebabs occasionally so that the chicken becomes tender and slightly charred all over.
Arrange the chicken kebabs on a warmed platter. Pour the dipping sauce into a small bowl and serve straight away.