DEIR AL BALAH, Gaza Strip — Aid groups are raising new alarm over Israel’s blockade of the war-ravaged Gaza Strip, where it has barred entry of all food and other goods for more than six weeks. Thousands of children have become malnourished, and most people are barely eating one meal a day as stocks dwindle, the United Nations says.

The only other way to get food in Gaza is from markets. But most cannot afford to buy there because of spiraling prices and widespread shortages, meaning humanitarian aid is the p