We study the Leibniz nn-algebra Un(L), whose multiplication is defined via the bracket of a Leibniz algebra L as [x1,…,xn]=[x1,[…,[xn-2,[xn-1,xn]]…]]. We show that Un(L) is simple if and only if L is a simple Lie algebra. An analog of Levi's theorem for Leibniz algebras in Un(Lb) is established and it is proven that the Leibniz n-kernel of Un(L) for any semisimple Leibniz algebra L is the n-algebra Un(L).