Tens of thousands of people have fled west Mosul since Iraqi forces launched an operation to retake it from Daesh on Feb. 19, pushing into the area from the south.
"Unfortunately, there is a clear shortfall in the work of these (UN) organizations," said Jassem Mohammed al-Jaff, the minister of displacement and migration.
Asked to elaborate, Jaff said: "The United Nations talks a lot but the efforts being made are little, despite the huge amount of money in their possession."
More than 50,000 people have fled west Mosul since the push to retake it was launched, Jaff said.
The UN, which has been providing shelter, food and other assistance to Iraqis who have fled Mosul during the nearly five-month-long battle, said it is working as fast as possible to help those displaced.
"The top priority for humanitarians is to make sure that there is sufficient capacity at emergency sites to deal with the number of civilians who are fleeing western Mosul," said Lise Grande, the UN's humanitarian coordinator in Iraq.
"In the past several weeks, we have been rushing to... construct that capacity, and we are redoubling our efforts now," Grande said.
Daesh overran large areas north and west of Baghdad in 2014, but Iraqi forces and other assistance have since regained most of the territory they lost to the terrorists.
The battle to retake Mosul -- the last Daesh-held city in Iraq -- was launched on Oct. 17.
More than 190,000 people are currently displaced as a result of the battle for Mosul, while more fled but have since returned to their homes, according to the International Organization for Migration.
Iraqi forces recaptured east Mosul in January, and have now set their sights on the smaller but more densely-populated western side of the city.