Russia's invasion of Ukraine could cause global food shortages in the coming months, the UN has warned.

Secretary-General Antonio Guterres said the war had worsened food insecurity in poorer nations due to rising prices.

The world could face famines that last for years if Ukrainian exports are not restored to pre-war levels, he added.

The conflict has cut-off supplies from Ukraine's ports, which once exported vast amounts of sunflower oil as well as cereals such as maize and wheat.

This has reduced the global supply and caused the price of alternatives to soar. Global food prices are almost 30% higher than the same time last year, according to the UN.

Speaking in New York on Wednesday, Mr Guterres said the conflict "threatens to tip tens of millions of people over the edge into food insecurity followed by malnutrition, mass hunger and famine".

"There is enough food in our world now if we act together. But unless we solve this problem today, we face the spectre of global food shortage in the coming months," he added.

He warned that there was no effective solution to the food crisis without reintegrating Ukraine's food production, as well as the fertiliser produced by Russia and Belarus, into the global market.