Gorakhpur, India (CNN) Prime Minister Narendra Modi started his Independence Day speech Tuesday with a call for the country to stand shoulder to shoulder with people of the city of Gorakhpur as they mourn the deaths of 68 children in a state-run hospital.

"In the last few days, our country's innocent children died in a hospital. In these times of crisis, these times of sadness, as all 1.5 billion of our countrymen give their condolences, I am with you all," Modi said.

Authorities in the northern state of Uttar Pradesh, the country's most populous state, are investigating why dozens of children died over seven days last week in the Baba Raghav Das (BRD) Medical College.

A 900-bed government hospital, BRD serves as a primary treatment facility for 20 million people in Uttar Pradesh and surrounding areas.

Parents say their children were starved of oxygen when tanks ran out because the supplier's bills hadn't been paid.

The Uttar Pradesh government said a lack of oxygen wasn't to blame and has appointed a high-level committee to investigate the deaths.

The children were suffering from acute encephalitis syndrome, also known as AES, according to India's Ministry of Health. The condition is characterized by inflammation of the brain caused by a range of microbes, typically viruses. In acute cases, patients often require assistance to breathe.

A scene from the ICU unit (ward 100) at BRD Medical College in Gorakhpur, Uttar Pradesh.

'It wasn't working'

Bandana Devi believes her three-and-a-half-year-old daughter Shivani died at the hospital because of a lack of oxygen.

"When she got into more critical condition, only then they put her on oxygen. I held the oxygen pipe and saw it wasn't working. I checked it with my hands, it wasn't working," she said.

According to CNN Affiliate News18, 60 children died between August 7 and 11. Since then, 8 more have been confirmed dead, including up to four on Monday, according to Dr. Kafeel Khan, the former head of the encephalitis ward who was relieved of his role on Sunday August 13

Khan had been called a hero for attempting to save lives by driving to a private nursing home in a bid to get more oxygen.

Nurses examining the patients at wad L of the ICU at BRD Medical College in Gorakhpur, Uttar Pradesh.

However, on Monday, he confirmed to CNN he was no longer employed at the government medical facility, but did not disclose why.

His efforts to find extra oxygen supplies were dismissed by KK Gupta, director-general of medical education in Uttar Pradesh, who has been stationed at BRD since Sunday and is helping to lead the investigation, according to CNN Affiliate News18.

"Dr. Khan has not done something great by providing three cylinders when 52 cylinders were already available ... there is nothing heroic about it," said Gupta, referencing what he claims was the hospital's existing oxygen supply.

Khan himself has denied that the children died due to a lack of oxygen. Khan said most of the children's death certificates cite lung failure, cardiac arrest and multiple organ failure as the cause of death. No post-mortems have been conducted, he added.

The state government have so far not commented on the claims, stating only that the investigation is ongoing.

Rajiv Mishra, the head of BRD Medical College, was suspended on August 12 after the deaths became public.

At a press conference, Mishra said he had tendered his resignation before he was suspended, and said he accepted moral responsibility for the deaths as they occurred during his tenure.

Mohammad Zahid, who lost his five-and-a-half year old daughter Khushi, holds his daughter's photograph in Gorakhpur in the Indian state of Uttar Pradesh, on August 14.

Hundreds of deaths 'normal'

Uttar Pradesh Health Minister Siddharth Nath Singh told reporters Friday that a large number of deaths are "very normal" in August.

He said 567 children had died at the hospital in August 2014. And as many as 668 and 587 in August 2015 and 2016.

The minister said that, as is the case with many medical colleges, many patients come to BRD Medical College after the first line of treatment fails.

An Indian woman looks after her child at the encephalitis ward on August 14.

Outbreaks of AES tend to coincide with the monsoon and post-monsoon period when there's more water around for mosquitoes to breed. It causes an acute onset of fever and can cause mental confusion, disorientation, delirium, or coma.

The condition is endemic in Uttar Pradesh where it led to 3,422 deaths between 2009 and 2015

'I do not want to stay at this hospital anymore'

Some of the parents of children still being treated in the hospital are trying to get them discharged.

Jonhai Devi, 63, traveled more than 80 miles (130 kilometers) from the neighboring state of Bihar to bring her three-year-old grandson Prince for treatment.

Now, two weeks later, she's trying to get him moved.

"I think my grandson is well now and the fever will go down with time. There is a local doctor in our village who is very good in treating patients with fever. I do not want to stay at this hospital anymore," Devi said.

Mohammad Kaimuddin Ansari and his son.

However, Prince's doctors say it's too risky for him to leave.

"How can we discharge a patient who has not yet recovered and the condition is critical," said junior resident doctor Radhey Shyam Singh.

"We cannot afford even a single death and all the doctors here are trying their best to give better treatment and special care to every child. Prince still needs to be here," he said.

Jonhai Devi is not the only worried relative who is trying to get a child discharged from hospital.

Mohammad Kaimuddin Ansari, 33, brought his son to the hospital from a city 31 miles (50 kilometers) away last Monday for the AES treatment of AES.

Indian relatives of patients wait outside the encephalitis ward at the Baba Raghav Das Hospital in Gorakhpur on August 14.

They don't have much money -- he makes a living as a farmer and carpenter.

"I want to take my child to some private hospital, no matter how expensive the hospital is. I cannot see my child dying," he said.

"I will sell my land, my house, my motorcycle and everything but I will save my child."