The Center for Science in the Public Interest had long rated sucralose as "safe" but is now placing it in the "caution" category in its Chemical Cuisine Guide to Food Additives.
The move comes after a review of an unpublished Italian study which has reportedly found the sweetener causes leukemia in mice.
The public safety group says consumers should avoid saccharin and aspartame, too.
The group says sweeteners made from Stevia are "safe," but deserve better testing.
