  Aims. We present the first results of an ongoing project devoted to the
search of giant radio halos in galaxy clusters located in the redshift range
z=0.2--0.4. One of the main goals of our study is to measure the fraction of
massive galaxy clusters in this redshift interval hosting a radio halo, and to
constrain the expectations of the particle re--acceleration model for the
origin of non--thermal radio emission in galaxy clusters. Methods. We selected
27 REFLEX clusters and here we present Giant Metrewave Radio Telescope (GMRT)
observations at 610 MHz for 11 of them. The sensitivity (1$\sigma$) in our
images is in the range 35--100~$\mu$Jy beam$^{-1}$ for all clusters. Results.
We found three new radio halos, doubling the number of halos known in the
selected sample. In particular, giant radio halos were found in A 209 and RXCJ
2003.5--2323, and one halo (of smaller size) was found in RXCJ 1314.4--2515.
Candidate extended emission on smaller scale was found around the central
galaxy in A 3444 which deserves further investigation. Furthermore, a radio
relic was found in A 521, and two relics were found in RXCJ 1314.5--2515. The
remaining six clusters observed do not host extended emission of any kind.
