Minimal algebraic groups with finite center

An algebraic infinite $K$-group with finite center is called minimal if all its proper $K$-subgroups have infinite center. We prove that every nonsolvable minimal $K$-group is $K$-isomorphic to the special orthogonal group $SO_{3,f}$ or to the spinor group $Spin_{3,f}$ of a quadratic anisotropic $K$-form $f$ in three variables.