Deep magma accumulation near the crust-mantle boundary (21 km depth) at the Krafla volcanic system is suggested from InSAR observations. A best fit model, derived from four interferograms covering 1993--1999, comprises an opening dike, representing plate spreading and post-rifting deformation, and two Mogi sources. A Mogi source deflating at a rate of ~0.3 ¿ 106 m3/yr coincides with the shallow Krafla magma chamber while a deeper inflating Mogi source, further north, at 21 km depth, inflates at a rate of ~26 ¿ 106 m3/yr. The inflating source is at or near the crust-mantle boundary as identified by seismic studies and is interpreted as accumulating magma.