CAIRO (Reuters) - Food security in the Middle East and North Africa is quickly deteriorating because of conflict in several countries in the region, the United Nations said on Thursday.  In those hardest hit by crises   Syria, Yemen, Iraq, Libya and Sudan   an average of more than a quarter of the population was undernourished, the U.N. s Food and Agriculture Organization said in its annual report on food security. A quarter of Yemen s people are on the brink of famine, several years into a proxy war between the Iran-aligned Houthis and the Saudi-backed government of President Abd-Rabbu Mansour Hadi that has caused one of the worst humanitarian catastrophes in recent times. The report focused on changes to food security and nutrition across the region since 2000. It said that undernourishment in countries not directly affected by conflict, such as most Gulf Arab states and most North African countries including Egypt, had slowly improved in the last decade. But it had worsened in conflict-hit countries.  The costs of conflict can be seen in the measurements of food insecurity and malnutrition,  the FAO s assistant director-general Abdessalam Ould Ahmed said.  Decisive steps towards peace and stability (need to be) taken.  Several countries in the region erupted into conflict following uprisings in 2011 that overthrew leaders in Tunisia, Egypt and Libya. Syria s civil war, which also began with popular demonstrations, has killed hundreds of thousands of people and made more than 11 million homeless. 