U.S. President Barack Obama returns from the gym at Marine Corps Base Hawaii in Kaneohe, Hawaii, on Boxing Day. (Kevin Lamarque/Reuters)

U.S. President Barack Obama signed a benefits bill on Sunday that will help police, firefighters and other emergency workers who became ill after working in the area around the World Trade Center towers that collapsed on 9/11.

The James Zadroga 9/11 Health and Compensation Act, which amends the Public Health Service Act to provide extra medical and other benefits to first-responders at the site of the Sept. 11 attacks, was one of the last measures Congress passed before adjourning in December.

"We will never forget the selfless courage demonstrated by the firefighters, police officers and first responders who risked their lives to save others," Obama said in a statement. "I believe this is a critical step for those who continue to bear the physical scars of those attacks."

The bill is named after a New York Police Department detective who worked at Ground Zero and died of a respiratory illness in 2006.

Zadroga and others were exposed to clouds of toxic fumes, dust and smoke. Many have since fallen very ill and dozens have died, with exposure to toxic chemicals at the site believed to be a major factor.

New York City Mayor Michael Bloomberg and Police Commissioner Raymond Kelly were among several politicians and officials who hailed the passage of the bill.

"The Sept. 11, 2001, terrorist attacks were an attack on America by a foreign enemy and addressing its health impacts is a national duty," Bloomberg said.

The bill faced opposition in Congress as Republicans repeatedly blocked the legislation. Some called it a New York slush fund, while others opposed increasing Washington's already massive deficit of $1.3 trillion US.

They dropped their opposition after lawmakers struck a compromise to reduce the costs.

The $4.2 billion measure will be paid for with a fee on some foreign companies that get U.S. government procurement contracts.

There was no signing ceremony for the bill. Obama signed the bill Sunday from Hawaii where he is vacationing with his family.

With files from The Associated Pres