Four time series of IRIS data (4 to 6 months) have been used to obtain improved measurements of the low degree (l=1,2,3) rotational splitting frequencies. Assuming that the rotation law is known in the outer layers of the Sun, we investigate the implications of IRIS splittings for the central regions. Both a one-shell and a two-shell rotation model have been considered in the solar core. A core rotating slightly faster than the outer radiative envelope provides the best fit to the data. Some evidence for the reliability of the observations is shown by the visibility of differential rotation in the l=3 multiplets.