President Barack Obama urged Congress Wednesday "out of an abundance of caution" to boost funding to fight swine flu by an extra two billion dollars 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 two billion dollars," 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 Wednesday 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 Organization showed Wednesday.
The four new deaths in New York and Chicago, which were not yet included in the CDC's report, raise the global tally to 121.
Separately Obama also asked for 200 million dollars more to address "the serious humanitarian crisis developing in Pakistan" which has displaced more than 2.5 million people.
US Secretary of State Hillary Clinton already announced in May an emergency aid to Pakistan of more than 100 million dollars to help those fleeing the fighting against Taliban militants in the Swat Valley.
The funds, if approved, will be added to the 2009 supplemental budget being debated by US lawmakers.