VATICAN CITY: Pope Francis appealed to authorities on Wednesday to lift a block on exports of wheat from Ukraine, saying the grain could not be used as a "weapon of war".

Many millions of people, particularly in the world's poorest countries, depend on wheat from Ukraine, the pope told a general audience of thousands of people gathered in St. Peter's Square, calling for the block to be lifted.

The United Nations, which says a global food crisis is worsening, is trying to broker a deal to unblock Ukraine's grain exports, though Western leaders have blamed Russia for holding the world to ransom by blockading Ukrainian ports.

"The blocking of exports of wheat from Ukraine is very worrying because the lives of millions of people depend on it, especially in poorer countries," the pope said.

"I make a heartfelt appeal so that every effort is made to resolve this problem, to guarantee the universal right to nutrition. Please! Do not use wheat, a basic foodstuff, as a weapon of war," he added, to applause from the crowd.

Besides the death and devastation sown by Russia's invasion of Ukraine, the war and the West's attempt to isolate Russia as punishment have sent the price of grain, cooking oil, fertiliser and energy soaring, hurting global growth.

The pope has often condemned the invasion and the bloodshed caused by what Moscow calls a "special military operation".

But Wednesday was the first time that he spoke in detail of the global food crisis it has brought.

Ukraine is desperately trying to export its vast stores of grain by road, river and rail to help avert the crisis, but has no chance of hitting its targets unless Russia lifts a blockade of its Black Sea ports, an agriculture official said last week.