GENEVA — Hundreds of young children have died from disease and malnutrition in the desert camp holding families of Islamic State fighters in northeast Syria, United Nations investigators said on Tuesday, warning that international inaction on the situation risked incubating a new wave of extremism.

The Commission of Inquiry, created by the United Nations Human Rights Council that is monitoring the conflict in Syria, said at least 390 children had died of preventable causes in the first half of the year while in, or on their way to, Al Hol, the camp set up to take in families fleeing the last strongholds of the Islamic State in Syria.

Their deaths exposed the “intolerable” conditions for the 70,000 people, more than 90 percent of them women and children, who are crammed into the Kurdish-run camp, with little access to medicine and food.

Their plight highlighted international paralysis over what to do with the residents, including 11,000 foreigners from dozens of countries, many of them still fervent supporters of Islamic State ideology, who have been shunned by their governments and in some cases stripped of their nationality.