South Korean officials said Thursday they will issue warnings on the bird flu drug Tamiflu, the second Asian nation to do so after Japan following reports of abnormal behaviour by young users.

The alert notices will advise doctors to monitor patients for any sign of psychological side-effects after a series of incidents in Japan -- including suicides -- raised questions over the blockbuster drug.

Swiss pharmaceutical Roche has repeatedly denied any connection between the incidents and its drug, which is often prescribed for seasonal flu.

Japan said Thursday that it had no plans to stop stockpiling Tamiflu for a possible avian flu outbreak, while several other Asian nations which stock or prescribe the drug say they do not intend to issue alerts for the moment.

Nevertheless, the reports have raised concerns because of the prevalence of bird flu, which has killed at least 169 people across the world since the end of 2003, the vast majority of them in Asia.

"We plan to issue a special document to doctors and pharmacists that notifies them of recent reports of suicides and strange behaviour by people who have taken the drug," said Shin Joon-Soo, an official with South Korea´s Food and Drug Administration.

"The document will also advise medical experts to report immediately to officials when witnessing similar mental symptoms," Shin was quoted by Yonhap news agency as saying.

Tamiflu has come under investigation in Japan after dozens of people who took the drug killed themselves. In a recent case, a 14-year-old boy leapt to his death last month from the 11th floor of an apartment block.

"It´s hard to say what the link between Tamiflu and the deaths is," said Professor Katsuhisa Nakajima at Nagoya City University Medical School.

"But it seems that once it comes into contact with the nervous system it has adverse effects," he added.

Japan on Wednesday instructed Roche´s Japanese subsidiary to warn against prescribing it for teenagers, although an investigation last year by the US Food and Drug Administration into the deaths concluded there was no link.

Tokyo buys more than 60 percent of the world´s supply of Tamiflu, which is considered a frontline drug against a potential pandemic of bird flu or other forms of influenza.

Earlier this month the health ministry said it would increase its stocks to cover a total of 28 million people in the event of a bird flu epidemic, and a spokesman Thursday said that plan had not changed.

"The Tamiflu that is stocked is not used for the popular form of influenza but for bird flu, against which we have no other weapon," he added.

In Indonesia, the country worst hit by bird flu with a human death toll of 66, the health ministry said it would not issue warnings.

"We do not detect any abnormal behaviour from recipients of the drug," I Nyoman Kandun, a senior health ministry official, told AFP, adding that more than 1,000 doses of the drug had been administered in the country.

Singapore said it was closely monitoring the overseas reports of abnormal behaviour and would take action if needed.

Suwarin Chaturapit, a deputy director at the Health Sciences Authority, said there was still no "direct causal link" between such behaviour and Tamiflu.

In the Philippines, where Tamiflu is administered as a regular antiviral medicine, a spokesman for the health department´s disease control centre said there were no plans to issue warnings similar to those in Japan.

Thailand produces its own generic version of Tamiflu, and a senior official at the Food and Drug Administration said they had not experienced any such side effects.

"We have never had any evidence of such effects," the official said, adding though that doctors would be vigilant.