Parents of at least 35 children who have died in a hospital in northern India over the past three days have alleged the fatalities were due to a lack of oxygen supply in the children's ward.
They said the oxygen supply to the ward ran out on Thursday night and relatives were given self-inflating bags to help the children breathe.
"That's the time when the death of the children peaked," said Mritunjaya Singh, whose seven-month old son was admitted to the hospital and was not among the dead.
The Uttar Pradesh government has ordered an investigation.
District Magistrate Rajiv Rautela said on Saturday the deaths of the children being treated for different ailments at the Baba Raghav Das Medical College Hospital in Gorakhpur city in Uttar Pradesh state were due to natural causes.
He denied that the lack of oxygen led to their deaths.
Prashant Trivedi, the state's top health official, admitted there was a problem in the pipeline supplying oxygen.
"But the situation was managed through oxygen cylinders. The hospital administration has enough supply of cylinders in its stock. So the report about death of children because of oxygen issue is false," Mr Trivedi said.
The parents said the company that supplies oxygen to the hospital had earlier threatened to stop oxygen distribution unless the government paid their long overdue bills.
Rautela said that the hospital owed 6.8 million rupees (£81,900) to the company, but added that it had adequate numbers of oxygen cylinders.
Some of the children had been treated for a which runs from June till September.
The hospital, which has become a major centre for children with encephalitis, has treated nearly 370 cases in the last two months. Of these, 129 children had died, said Satish Chandra, a hospital spokesman.
Gorakhpur is located 185 miles south-east of the state capital, Lucknow.