  In the recently published 3FGL catalogue, the Fermi/LAT collaboration reports
the detection of $\gamma$-ray emission from 3034 sources obtained after four
years of observations. The nature of 1010 of those sources is unknown, whereas
2023 have well-identified counterparts in other wavelengths. Most of the
associated sources are labelled as blazars (1717/2023), but the BL Lacs or FSRQ
nature of 573 of these blazars is still undetermined.
  The aim of this study was two-fold. First, to significantly increase the
number of blazar candidates from a search among the large number of Fermi/LAT
3FGL unassociated sources (case A). Second, to determine the BL Lac or FSRQ
nature of the blazar candidates, including those determined as such in this
work and the blazar candidates of uncertain type (BCU) that are already present
in the 3FGL catalogue (case B).
  For this purpose, multivariate classifiers were trained using samples of
labelled sources with no caution flag from the 3FGL catalogue and carefully
chosen discriminant parameters. The decisions of the classifiers were combined
in order to obtain a high level of source identification along with well
controlled numbers of expected false associations. Specifically for case A,
dedicated classifications were generated for high and low galactic latitude
sources, in addition, the application of classifiers to samples of sources with
caution flag was considered separately, and specific performance metrics were
estimated.
  We obtained a sample of 595 blazar candidates among the unassociated sources
of the 3FGL catalogue. We also obtained a sample of 509 BL Lacs and 295 FSRQs
from the blazar candidates cited above and the BCUs of the 3FGL catalogue. The
number of expected false associations is given for different samples of
candidates. It is, in particular, notably low ($\sim$9/425) for the sample of
high-latitude blazar candidates from case A.
