Advanced scenarios featuring Internal Transport Barriers (ITBs) need to be extended to densities towards the Greenwald value in order to demonstrate their reactor relevance. It is difficult to access this regime since NBI deposition becomes less efficient in injecting particles and torque into the plasma core and high additional current drive power must be applied to maintain the optimized magnetic shear needed for stabilizing the turbulence. Steep internal density gradients, created by pellets, can substantially contribute to turbulence stabilization, and can efficiently drive the off axis bootstrap current that keeps the magnetic shear small or negative. This paper describes experiments performed on JET aimed at the production of high density ITBs by means of pellet injection. The basic scenario is illustrated in Fig.1. After a LH prelude, aimed at producing a reversed shear configuration, a pre-fuelling gap of about 1s follows which can be ohmic or heated with a moderate amount of NBI power (~4 MW). During this gap, pellets are injected in order to prepare a high density target for the main heating phase characterised by the injection of a comparable amount of NBI and ICRH power. When conditions are optimised, high density barriers are formed at similar electron and ion temperatures. These barriers can last several hundreds of milliseconds and tend to decay either due to MHD events or to the flattening of the density profile. Attempts to refuel the ITB during the main heating have given encouraging results.