The global body says 12,720 new cases have been reported since Wednesday — about half of them in the United States.

WHO says Britain, Chile, Mexico, Philippines also reported large numbers of new cases.

Health experts say the number of cases reported to WHO is far below the figure of actual infections because many are mild and never diagnosed.

WHO is working on mathematical models to estimate the real number of infections.

According to the agency’s swine flu update Friday, the number of deaths increased by 50 to 382.

Most of the deaths occurred in the US.

The fatality is the second in the Asia-Pacific region related to swine flu, following the death of a man in Australia on Friday.

Philippine Health Secretary Francisco Duque III said the woman’s chronic heart disease was aggravated by severe pneumonia. She started to have flu-like symptoms such as dry cough, fever, chills and difficulty breathing two days before her death on June 19.

A throat swab revealed she was also infected with the swine flu virus.

Duque said post-autopsy findings disclose that the death was caused by heart failure “aggravated by severe pneumonia either bacterial, viral or both.”

Given the available information, health authorities cannot conclude that the death is due to H1N1. In other countries that have reported swine flu deaths, the majority have had pre-existing conditions, he added.

Duque said the Philippines has 17 more confirmed swine flu cases, bringing the total to 445 — though 84 percent of the total cases have already recovered.

Australian authorities on Sunday listed a 26-year-old Aboriginal man who died in the southern city of Adelaide on Friday as a “suspected” swine flu death. Although the man had tested positive for the virus, authorities doubt it killed him because he also had pre-existing chronic diseases.

Meanwhile, the first case of swine flu was reported in Iran. A report on the Web site of the Iranian Health Ministry said the patient is a 16-year-old Iranian boy who lives in the United States and arrived in Iran with his parents.

The report did not identify the boy. It said the case was detected when he arrived at an airport in Iran with some symptoms of lung infection. The report says the boy was quarantined and he and his parents received medical care.