Is Altair from Assassin's Creed an atheist?

Given the state of the world at the time and the part of it in which he lives, in addition to what he does, what he experiences and what he knows, it is hard to see him as a pure atheist. He may be somewhat agnostic or cynical or religion, but it is evident he must have some belief in a higher power.

At no point in the game does he explicitly say that he is an atheist. However, he is not shown as being religious, either. He should be thought of as an agnostic in that respect.