Millions of Iraqis are driven outside their homes after the intensive fighting all over the country, but the humanitarian aids do not reach the most dangerous places and people displaced in places away from aid agencies reach, said the Medecins Sans Frontieres (MSF).
At least 3 million people are displaced after fleeing the central and northern areas of the country, in particular Anbar, Nineveh, Salah al-Din, Kirkuk and Diyala, the group said.
"Despite the magnitude of people's needs, the humanitarian response has been mostly concentrated in safer areas, such as the Kurdistan region of Iraq," said Fabio Forgione, MSF's head of mission in Iraq.
Many Iraqis in the grey zones in the north of Iraq in Mosul city and between Baghdad and Anbar are suffering of degrading humanitarian circumstances, without clean water or basic healthcare in damaged homes. Most of them have been displaced many times.
"Iraq is experiencing its worst humanitarian crisis of recent decades," said Forgione in a statement late on Monday.
The United Nations launched last week its humanitarian response plan for 2015 to help Iraq. The UN asked for $500 millions as it estimates that at least more than 25 percent of the Iraqı population which is about 8.2 million Iraqis will need a humanitarian aid this year.
Last month ISIS captured the Ramadi city, capital of Anbar province, forcing thousands of Iraqis to flee their homes.
After ISIS captured the city of Ramadi, the Iraqi army started building up positions around the city and preparing for a battle to retrieve it.
"We are very alarmed by the prospect of violence spreading to other densely populated cities, triggering yet more displacement," said Forgione.