While grain silos in many Western countries may overflow this winter, tens of millions of people risk going without food as hunger is being used more than ever as a weapon ofwar.

More than 50 million people living in 17 conflict-ridden countries are in "severe food insecurity", two UN agencies warned recently.

The protracted conflicts in Yemen and Syria place those two nations at the top of the list established by the Food and Agriculture Organization (FAO) and the World Food Programme (WFP).

In Yemen, 14 million people - over half the population - are now considered to be facing a food crisis or emergency.

Meanwhile in Syria, 8.7 million people or 37 percent of the pre-conflict population, "need urgent food, nutrition and livelihoods assistance", in particular aid to farmers, said the agencies.

The same goes for parts of northeastern Nigeria, which has borne the brunt of an insurgency by Boko Haram islamists since 2009, and where the aid group Doctors Without Borders estimates half a million people face a humanitarian catastrophe.

Thousands of hungry people forced from their homes by fighting there had to wait until the end of July to receive their first food aid.

Meanwhile, most of the world's top wheat producers are enjoying bumper crops, pushing prices down on global commodity markets and benefiting countries like Egypt that are dependent upon imports.

But for countries gripped by conflict, importing food is logistically difficult if not impossible and at prices out of the reach of most of the population which have lost their livelihoods. Maintaining local agricultural production, even traditional small-scale farms, thus often becomes critically important for reducing hunger while helping keep down the number of refugees, said the head of the FAO's emergency unit, Dominique Burgeon.

In certain parts of Syria this year people who have been displaced from other regions are helping till the fields and take in the harvest.

Even so, that hasn't saved the agricultural sector, on which four-fifths of the rural population depends, from collapse.

In June, Pope Francis condemned the fact it is often more difficult to deliver humanitarian aid than to obtain weapons.

"It makes no difference where arms come from; they circulate with brazen and virtually absolute freedom in many parts of the world," said the pontiff during a visit to the WFP's headquarters. "As a result, wars are fed, not people."