Guterres is on the second day of a visit to Iraq, after meeting with top officials in Baghdad on Thursday.
"We don't have the resources that are necessary to support these people and we don't have the international solidarity that is needed," Guterres told journalists during a visit to the Hasan Sham Camp.
"Unfortunately, our programme here is only funded at eight percent; that shows how limited our resources are," he said.
"These people have suffered enormously, and they go on suffering. We need more solidarity from the international community," he said.
Guterres is on the second day of a visit to Iraq, after meeting with top officials including Prime Minister Haider al-Abadi in Baghdad on Thursday.
His visit comes as Iraqi forces battle to retake second city Mosul, which was seized by the Islamic State jihadist group in 2014.
The fighting has sparked major humanitarian concerns, killing hundreds of civilians and displacing more than 200,000 since the operation to retake the city's western side began last month.