(CNN) -- Nearly half the children in Yemen's troubled northern province are suffering from malnutrition, the humanitarian agency UNICEF warned Wednesday.

The United Nations children's agency supported a government screening that found 50 percent of the 26,246 children in five districts of Saada to be at risk of death because of inadequate nutrition. In some areas, as many as three out of four children were acutely malnourished.

"Malnutrition is the main underlying cause of death for young children in Yemen, and therefore this grim situation could spell disaster for the children of Saada," said Geert Cappelaere, the UNICEF representative in Yemen.

"As winter approaches, thousands of children are at serious risk if we are not able to act immediately," Cappelaere said.

Malnutrition was already a problem throughout Yemen, which is one of the poorest countries in the region and is hampered by high unemployment, inflation, drought and severe food shortages. The World Food Programme estimates that almost 3 million people in Yemen face severe food insecurities.

In Saada, the situation was aggravated by a protracted conflict between government forces and militant Shiite rebels, UNICEF said.

Efforts to deliver food and other basic relief items have been impeded by the "extremely volatile security situation," the agency said.

The United Nations estimates that more than 300,000 Yemenis have been displaced by six rounds of fighting since 2004 between the government and Houthi rebels demanding autonomy for their community. Though Yemen is mostly Sunni, the rebels are followers of slain Shiite cleric Hussein al-Houthi.

A cease-fire has been in effect since February, but U.N. agencies say the truce is shaky.