"We see no evidence at all that there is widespread occurrence of antiviral resistance," the U.N. health agency's pandemic flu expert, Keiji Fukuda, told a news conference.

Antiviral drugs such as oseltamivir, marketed by Swiss drugmaker Roche Holding as Tamiflu, have encountered only sporadic resistance from H1N1, known as swine flu, he said.

(Reporting by Jonathan Lynn)