Moscow and Tehran have supported Syria's government with ground troops and airstrikes.
Zeid Ra'ad Al Hussein says "deliberate starvation" is being used as a weapon of war.
A U.S.-Russia brokered cessation of hostilities has been in place since Saturday.
Dr. Khaled Mohammed details the continuing desperation of the town's population despite aid deliveries.
A new report shows that 11.5 percent of Syrians have been physically affected by the war.
A convoy of 50 aid trucks will travel to the encircled Syrian town on Thursday.
Emergency food supplies will help people who are right now starving to death.