Authorities claiming that the arson attacks on rail infrastucture were probably carried out by "the ultra-left".

I don't know, but it doesn't seem very credible to me that an actual leftist would do that *and then not claim it*. It doesn't really make sense in the context of leftist politics - you'd want to be making a point, and ensure it is clearly understood.

Unlike right-wing groups, which thrive on fear and blame, I don't see that leftist groups really have much to gain from just causing unspecified chaos... that's not how leftist politics work.