South Korea has spotted a suspected case of swine flu in a citizen just back from a trip to Mexico, Yonhap news agency quoted a government official as saying Tuesday (April 27).

"A South Korean citizen who recently returned from a trip to Mexico has been classified as a possible swine flu patient," the official said on condition of anonymity.

No further details were immediately available.

On Monday officials said the country would double its stockpile of Tamiflu and other anti-influenza drugs to a quantity sufficient to treat five million people.

With the likely human swine flu death toll in Mexico, the epicenter of the outbreak, now standing at 149, the World Health Organization has raised its flu pandemic alert level.