WASHINGTON - US President Barack Obama on Tuesday asked Congress for an additional US$2 billion (S$2.8 billion) to address the H1N1 flu strain circulating around the United States.

In a letter to House of Representatives Speaker Nancy Pelosi, President Obama said he was requesting the additional funding 'out of an abundance of caution.' President Obama had already asked Congress for US$1.5 billion to buy additional antivirals, emergency equipment and for vaccine development.

He said the administration had learned much more about the H1N1 outbreak and the level of national response that could be necessary in the coming months.

'There also remains much uncertainty about the outbreak and its potential to return during the upcoming flu season in the United States,' President Obama said in requesting the additional funds.

Cases of the new H1N1 flu virus have been found in all 50 US states and tests have confirmed the virus in more than 10,000 people across the country, US officials said on Monday.

Most of those hospitalised had underlying medical conditions that included lung disease, weakened immune systems and heart disease, and a smaller number had diabetes or were obese or pregnant.

At an emergency hearing in April, health officials told Congress that the funding sought by the Obama administration would be crucial if the flu virus spreads.

The H1N1 virus, which spreads easily and causes mostly mild disease, has been diagnosed in about 17,564 people in 64 countries, killing 115, according to the World Health Organisation. -- REUTERS