Ukraine and Russia have signed an UN-backed deal to allow the export of millions of tonnes of grain from blockaded Black Sea ports. The agreement potentially averted the threat of a catastrophic global food crisis. A signing ceremony at Dolmabahçe Palace in Istanbul was attended by UN secretary general António Guterres, who had played a key role during months of tense negotiations. The delegates of Russia and Ukraine were also present. Mr. Guterres said that the deal would open the way to significant volumes of food exports from Ukraine and alleviate a parallel food and economic crisis in the developing world.