UNITED NATIONS, April 13 (Reuters) -- Poor countries face economic ruin from simultaneous crises of food, energy and finance due to supply disruptions caused by Russia’s invasion of Ukraine, UN Secretary-General Antonio Guterres said on Wednesday. Russia is the world’s top exporter of combined oil and gas, and Russia and Ukraine are both major producers of grain, together accounting for around a third of global exports. World commodity prices have hit records, hurting countries that rely on imports. “The war is supercharging a three-dimensional crisis - food, energy and finance - that is pummeling some of the world’s most vulnerable people, countries and economies,” Guterres said.