A two-month-old baby is being treated in hospital for possible exposure to chemical weapons after an attack in Mosul thought to have been carried out by ISIS.

The baby is one of 12 people, including women and children, who have been treated since March 1 after the attack where Islamic State is fighting off an offensive by U.S.-backed Iraqi forces, the United Nations said on Saturday.

Although it is not known who is to blame for the attack, the mortars were apparently fired from ISIS held west Mosul.

Scroll down for video

A mother comforts her daughter Ranmea as they spend time in hospital after the chemical weapon attacks in Mosul

Dima Nazim, two-years-old, is a victim of IS chemical attack receives treatment in a hospital in Irbil, Iraq

Yasser Hamid Nadm, 11 years old is treated for possible exposure to chemical weapons agents in a hospital in Mosul

It is the first chemical attack in the battle for the ISIS stronghold.

The U.N.'s World Health Organisation has activated 'an emergency response plan to safely treat men, women and children who may be exposed to the highly toxic chemical,' with partners and local health authorities, the agency said in a statement.

It said all 12 patients had been received since March 1 for treatment which they are undergoing in Erbil, the capital of Iraq's Kurdish region, east of Mosul.

Thaier Hamed Nadm, 10 years old is treated for possible exposure after what is the first chemical weapons attack in the battle for the ISIS stronghold

Dima Nazim is among the youngest victims of the attacks, with a month-old baby also being treated for exposure

Yasser Hamid Nadm, 11. The attack appears to have come from the western side of Mosul, which is still an ISIS stronghold

A doctor in western Irbil said on Saturday that 10 people with injuries caused by chemicals have been admitted to his hospital over the last two days. Above, Yasser, 11

Thaier Nazim, 10. A UN World Health Organisation health plan has been activated following the attack

Four of them are showing 'severe signs associated with exposure to a blister agent'. The patients were exposed to the chemical agents in the eastern side of Mosul.

According to the BBC, ISIS have long been suspected of making and using crude chemical weapons in territory it controls in Iraq and neighbouring Syria.

The International Committee of the Red Cross (ICRC) said on Friday that five children and two women were receiving treatment for exposure to chemical agents.

The ICRC statement did not say which side used the chemical agents that caused blisters, redness in the eyes, irritation, vomiting and coughing.

Ekhlas Meshal, 30, holds her injured two-month old child Ranmea, as she sits next to her injured two-year old daughter Dima

Ekhlas becomes emotional as she tries to comfort her young daughters who have both been hit by chemicals. The patients are showing severe signs associated with blister agents

The chemical agents cause blisters, redness in the eyes, irritation, vomiting and coughing

Nazim Hamid stands next to his injured son Yasir, 11, one of the young victims of the attack

Iraqi forces captured the eastern side of Mosul in January after 100 days of fighting and launched their attack on the districts that lie west of the Tigris river on February 19. The eastern side remains within reach of the militants' rockets and mortar shells.

Defeating Islamic State in Mosul would crush the Iraqi wing of the caliphate declared by the group's leader, Abu Bakr al-Baghdadi, in 2014, over parts of Iraq and Syria.

The U.N. Humanitarian Coordinator in Iraq, Lise Grande, called for an investigation.

'This is horrible. If the alleged use of chemical weapons is confirmed, this is a serious violation of international humanitarian law and a war crime, regardless of who the targets or the victims of the attacks are,' she said in a statement.

ICRC's regional director for the Middle East, Robert Mardini said: 'During the past two days, the hospital has admitted five children and two women showing clinical symptoms consistent with an exposure to a blistering chemical agent.

'The use of chemical weapons is absolutely prohibited under international humanitarian law. We are deeply alarmed by what our colleagues have seen, and we strongly condemn any use of chemical weapons, by any party, anywhere.'

An Iraqi man carries a girl as they walk down a road to flee Mosul today during an offensive by security forces to retake the western parts of the city from ISIS

Iraqi families walk down a road as they flee Mosul during the battle for the remaining ISIS stronghold

A woman carries her child as she seeks to get them both to a place of refuge away from the battle

As the battle continues to regain the ISIS stronghold, tens of thousands of people have fled west Mosul since Iraqi forces launched an operation to retake it from the Islamic State jihadist group on February 19, pushing into the area from the south.

An Iraqi minister sharply criticised UN efforts to aid civilians fleeing fighting in west Mosul, even as the United Nations insisted that providing such assistance was the 'top priority'.

Jassem Mohammed al-Jaff, the minister of displacement and migration said: 'Unfortunately, there is a clear shortfall in the work of these (UN) organisations.

'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.

An Iraqi special forces soldier mourns his colleague and friend after Islamic State militants shot dead another Iraqi special forces soldier during a battle in Mosul, Iraq

The battle for the ISIS stronghold is still being fought, displacing families and leaving hundreds of casualties

Grande, the UN's humanitarian coordinator in Iraq said: '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.

'In the past several weeks, we have been rushing to... construct that capacity, and we are redoubling our efforts now.'

IS overran large areas north and west of Baghdad in 2014, but Iraqi forces backed by US-led air strikes and other assistance have since regained most of the territory they lost to the jihadists.

The battle to retake Mosul - the last IS-held city in Iraq - was launched on October 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 Organisation 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.