  We considered 18 solar flares observed between June 2010 and July 2012, in
which high energy >100 MeV {\gamma}-emission was registered by the Large Area
Telescope (LAT) aboard FermiGRO. We examined for these {\gamma}-events soft
X-ray observations by GOES, hard X-ray observations by the Anti-Coincidence
Shield of the SPectrometer aboard INTEGRAL (ACS SPI) and the Gamma-Ray burst
Monitor (GBM) aboard FermiGRO. Hard X-ray and {\pi}0-decay {\gamma}-ray
emissions are used as tracers of electron and proton acceleration,
respectively. Bursts of hard X-ray were observed by ACS SPI during impulsive
phase of 13 events. Bursts of hard X-ray >100 keV were not found during time
intervals, when prolonged hard {\gamma}-emission was registered by
LAT/FermiGRO. Those events showing prolonged high-energy gamma-ray emission not
accompanied by >100 keV hard X-ray emission are interpreted as an indication of
either different acceleration processes for protons and electrons or as the
presence of a proton population accelerated during the impulsive phase of the
flare and subsequently trapped by some magnetic structure. In-situ energetic
particle measurements by GOES and STEREO (High Energy Telescope, HET) shows
that five of these {\gamma}-events were not accompanied by SEP events at 1 AU,
even when multi-point measurements including STEREO are taken into account.
Therefore accelerated protons are not always released into the heliosphere. A
longer delay between the maximum temperature and the maximum emission measure
characterises flares with prolonged high energy {\gamma}-emission and solar
proton events.
