Krull–Schmidt reduction of principal bundles in arbitrary characteristic

Let M be an irreducible projective variety defined over an algebraically closed field k, and let EG be a principal G-bundle over M, where G is a connected reductive linear algebraic group defined over k. We show that for EG there is a naturally associated conjugacy class of Levi subgroups of G. Given a Levi subgroup H in this conjugacy class, the principal G-bundle EG admits a reduction of structure group to H. Furthermore, this reduction is unique up to an automorphism of EG.