Peel kiwifruit, quarter lengthwise and cut into 1cm slices. Place in a medium-size stainless steel saucepan with a heavy base. Add lime/lemon juice.
Mix sugar and agar powder in a small bowl until well mixed and add to the fruit in the pan. Bring mixture to the boil and stir until sugar dissolves. Allow jam to boil rapidly (stirring occasionally) until most of the liquid evaporates, about 15 minutes. Jam should thicken slightly.
Cool and store in a clean, dry jar. Refrigerated, it will keep for 1-2 weeks.