UNITED NATIONS - UN Secretary-General Antonio Guterres is concerned by rising tensions between nuclear-armed states, warning "the world will lose an invaluable brake on nuclear war" with the expiration of the Intermediate-range Nuclear Forces Treaty (INF) on Friday."This will likely heighten, not reduce, the threat posed by ballistic missiles,"Guterres told reporters. "I strongly encourage the United States and the Russian Federation to extend the so-called 'New Start' agreement to provide stability and the time to negotiate future arms control measures."Guterres also said he was "troubled by growing friction" between the economies of the United States and China. He warned of the "possible emergence of two competing blocs – each with their own dominant currency, trade and financial rules, their own internet and artificial intelligence strategy, and their own contradictory geopolitical and military views."