The last remaining US-Russia nuclear arms pact has ended, sparking major fears of a new global atomic weapons arms race. Termination of the 15 year-old New Strategic Arms Reduction Treaty comes at the worst time for world peace, according to experts. Signed in 2010 it was aimed at halting the threat of a catastrophic nuclear war . UN Secretary General António Guterres said it "marks a grave moment for international peace and security" and called on Russia and the US to negotiate "without delay.”