The compensation fund for victims of the 9/11 terror attack is running out of money and future payments will have to be cut by 50 to 70 per cent, officials have said.

September 11th Victim Compensation Fund special master Rupa Bhattacharyya said she was “painfully aware of the inequity of the situation” but vowed reduced funds would be paid out to every valid claim.

“I could not abide a plan that would at the end of the day leave some claimants uncompensated,” she added.

Nearly 40,000 people have applied to the federal fund for people with illnesses related to them being at the World Trade Centre site, the Pentagon or Shanksville, Pennsylvania, after the 2001 terror attacks there. About 19,000 of those claims are pending.

Nearly $5bn (£3.9bn) in benefits have been awarded out of the $7.3bn (£5.7bn) fund.

Ms Bhattacharyya said fund officials estimate it would take another $5 billion (£3.9bn) to pay pending claims and future claims that officials anticipate will be submitted before the fund’s December 2020 deadline.

Officials determined that pending claims submitted by 1 February would be paid at 50 per cent of their prior value. Valid claims received after that date will be paid at just 30 per cent.

Members of Congress vowed to take action.

“This is devastating news to the thousands of sick and injured 9/11 responders and survivors who were promised, and have been counting on, being fully compensated for the losses they have suffered,” said Democrats Jerry Nadler and Carolyn Maloney and Republican Peter King said in a joint statement.

They said they would introduce legislation to make the compensation fund permanent and to compensate all legitimate claimants.

“Our bill would restore any cuts to awards, ensure that future eligible recipients are fully compensated, and make the VCF program permanent,” they said.

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The Senate’s most senior Democrat, Charles Schumer, said the fund is supposed to provide “peace of mind to those sickened after the horrific attack.”

“For too many, ailments and disease from exposure to that toxic airborne brew have taken years to show up and – as the need for the fund grows – the chance it may not have adequate resources to take care of our heroes is just unacceptable,” he said in a statement.

Thousands of construction workers, police officers, firefighters and others spent time working in the soot, often without proper respiratory protection, when the trade centre collapsed.

In the 17 years since, many have seen their health decline, some with respiratory or digestive-system ailments that appeared almost immediately, others with illnesses that developed as they aged, including cancer.

Scientists cannot say definitively whether toxins at the site gave people cancer. One study published last year found that overall mortality rates among nearly 30,000 rescue and recovery workers were not elevated. But researchers have raised concern an unusual number of suicides among first responders and more deaths than expected from brain cancers and non-Hodgkin’s lymphoma.

Ms Bhattacharyya said the volume of claims has increased over the past year, with more than 8,000 claims filed in the last four months.

Reasons for the increase include the long latency period for some cancers as well as an increase in applications by people who lived or worked near the trade centre but were not actively involved in recovery efforts, she said.