WASHINGTON (Reuters) - The U.S. State Department on Tuesday criticized Russian Foreign Minister Sergei Lavrov's comments about the potential of a nuclear war, saying loose talk about nuclear escalation was the "height of irresponsibility."

       Lavrov warned the West on Monday not to underestimate the elevated risks of nuclear conflict over Ukraine and said he viewed NATO as being "in essence" engaged in a proxy war with Russia by supplying Kyiv with weaponry.

       (Reporting by Simon Lewis and Humeyra Pamuk; Editing by Chris Reese)