United Nations Secretary-General Antonio Guterres called for an acceleration of Black Sea grain shipments from Ukrainian ports under a deal allowing safe wartime exports, a U.N. spokesperson said on Tuesday as Russia threatens to quit the pact next month. The United Nations and Turkey brokered the Black Sea Grain Initiative with Russia and Ukraine in July 2022 to help tackle a global food crisis worsened by Moscow's invasion of its neighbor and blockade of Ukrainian Black Sea ports.