President Barack Obama asked Congress today "out of an abundance of caution" to boost funding to fight swine flu by an extra $2 billion on top of $1.5 billion already requested.
In a letter to House Speaker Nancy Pelosi, Obama said since he had made his first request for funding in late April "we have learned much about the outbreak and the level of national response that possibly could be necessary in the coming months."
"Out of an abundance of caution, I ask Congress to consider an additional and contingent request for $2 billion," the US president wrote.
Obama stressed that Congress, which holds the nation's purse strings, should give him the "maximum flexibility to allow us to address this emerging situation."
The US toll from the new multi-strain swine flu hit 21 today as new deaths were reported in New York and Chicago.
More than 11,000 cases have been confirmed in the United States, according to latest figures from the Centers for Disease Control and Prevention.
Swine flu has now spread to 66 countries with 19,273 people known to have been infected since the disease was first uncovered in April, data from the World Health Organisation showed today.