During Antonio Guterres' visit to a camp for internally displaced people in Iraq, residents complained to him about the quality of drinking water and poor living conditions.
UN Secretary General Antonio Guterres on Friday appealed to the international community to boost aid for civilians fleeing the Iraqi city of Mosul.
Iraqi forces backed by US air strikes have been battling to retake the country's second-largest city, which fell under Daesh control in 2014.
"We don't have the resources necessary to support these people," Guterres said during a visit to the Hassan Sham camp, one of several centres outside Mosul packed with civilians who've escaped the fighting.
At least 355,000 residents have fled the fighting, according to the government.
Some 400,000 civilians remain trapped inside the densely-populated Old City where street battles have raged on for weeks.
During Guterres visit, which lasted about half an hour, residents complained to him about the quality of drinking water and the poor living conditions in the tents.
The UN and Iraqi authorities have been building more camps but struggle to accommodate new arrivals, with two families sometimes having to share one tent.
Many of the displaced have returned to their homes in areas retaken from Daesh, but some, like those from the neighbourhood of Saqr, have not yet been allowed by authorities to return.
Government forces and their allies have recaptured most of Mosul from Daesh during a six-month campaign.
Coalition positions have reached as close as 500 metres to the Al Nuri Mosque, from where Daesh leader Abu Bakr al Baghdadi in July 2014 declared the group's so-called caliphate spanning parts of Iraq and Syria.