hi doma,
there seems to be strong evidence that the syrian regime used the weapons.
that does not make the unlikely view impossible.
it is certainly perfectly reasonable to conclude something different than the us without saying the us admin is lying because it thinks its own view is highly likely to be correct.
in your view, i guess the us is also calling putin a liar.
folks disagree and it's okay.
no one calls you a liar for believing in an electric universe. and yet other folks think this ain't so. are you calling them liars?