Public Health Minister Mongkol na Songkhla yesterday said his ministry would enforce compulsory licensing on no more than five medicines in a bid to tackle the five main killer diseases.

Aids and heart diseases are among the top killers.

The ministry has already broken the patent of HIV/Aids drug efavirenz, sold by US-based pharmaceutical giant Merck under the trade names Sustiva and Stocrin.

It has been in negotiations with the patent holders of two other medicines - HIV drug Kaletra made by Abbott Laboratories, and the anti-clotting agent Plavix, made by Sanofi-Aventis and its local subsidiary.

Mongkol was speaking in a bid to refute reports that Thailand was going to break the patents of between 20 and 30 medicines.

Compulsory licensing is permitted under World Trade Organisation rules in national emergencies or justified non-commercial cases. Patent holders can receive some royalties.

"Compulsory licensing is used only where necessary. It is used on life-saving medicines," Mongkol said.

While admitting pressure was growing on his decision to push ahead with compulsory licensing, Mongkol vowed not to backtrack.

"We can't give in. There are patients' lives at stake," he said.

Mongkol said he would try to explain the reasons behind the ministry's move to all parties when he flew to the United States next week.

In the US, he is also scheduled to ink a deal with the Clinton Foundation and 16 other developing countries for bulk buying of drugs at a cheaper price.

Citing widespread violations of intellectual property rights, the US Trade Representative this week downgraded Thailand's trade status by putting it on the Priority Watch List.

The move was widely seen as retaliation against the use of compulsory licences to override patents on certain drugs.

Jon Ungphakorn and Nimit Tien-udom, respectively the secretary-general and director of the Aids Access Foundation, yesterday sought a meeting with Mongkol to give information on how some non-governmental organisations and US Congress members had reacted to the ministry's compulsory licensing.

According to Jon, three common questions concerned compulsory licensing being enforced by a military-installed government, the ministry not negotiating with drug companies before going ahead, and worries that the ministry planned to enforce compulsory licensing on up to 30 medicines.

"Some people have tried to link the enforcement of compulsory licensing to the fact that the government was installed by coup makers," Jon said.

He said a lobbying firm had spread misleading information on the ministry's use of compulsory licensing.

"Still, many organisations and US Congress members support us," Jon said.

He added that many developing countries such as Brazil, India and Argentina agreed with Thailand's compulsory licensing, while the US and Italy also enforced compulsory licensing.

In a related development, Prime Minister Surayud Chulanont has ordered the Commerce Ministry to work with the US embassy in Bangkok to prepare an action plan for removing Thailand from the Priority Watch List.

However, the plan will not include backtracking on the use of compulsory licensing to ensure access to certain life-saving medications.

Surayud said his government would get Thailand off the watch list.

It would find a "balanced" solution, he said. Flaws identified will be corrected but Thailand will not back down in areas where it had acted humanely, he said.

The ministry's decision to use compulsory licences - after 10 years of lobbying by Thai and international Aids groups - has been called a welcome precedent for the developing world and a crucial step in dealing with a global epidemic by many health activists.

Pharmaceutical companies and business associations have, however, condemned the use of compulsory licences, saying it threatens the patent system and medical research.

Surayud also responded to the rumour that ousted premier Thaksin Shinawatra was behind the decision to put Thailand on the watch list. If violations of intellectual property rights were brought to an end, other factors would be irrelevant, he said.