U.S. Ambassador to the United Nations Samantha Power Monday strongly challenged Russia’s defense of its invasion of Ukraine’s Crimea region as a human rights mission aimed at protecting the ethnic Russian population there.

Power, arguing in front of her Russian counterpart and other members of the U.N. Security Council, went further than other Obama administration officials have so far in condemning Russia’s actions over the weekend, saying Moscow’s rationale for violating Ukrainian sovereignty has “no basis in reality.”