what does "back to the barracks " here mean? Does it mean demonstrating?
The ceasefire is indeed extremely fragile, and we are calling upon the Syrian government to fully implement its commitments under the six-point plan, and this means withdrawal of all heavy armoury (and) from population centres and back to the barracks.

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It means that government forces should return to their bases.
"Barracks" refers to the place where military forces are based.
"Barricades" are what demonstrators/rioters erect in the streets.