GENEVA - The U.N. health chief urged countries on Monday to come up with new ways to make medicine for HIV/AIDS and other diseases more affordable in the world's poorest countries, without stifling innovation among pharmaceutical companies.

The World Health Organization's 193 member states are hoping to forge a global strategy on the highly divisive issues of drug development, patenting and pricing by the end of the week.

"People should not be denied access to lifesaving and health-promoting interventions for unfair reasons," said Dr. Margaret Chan, WHO's director-general, in opening the agency's first meeting devoted to the subject since May, when the United States walked out of a negotiating session and dissociated itself from a WHO resolution.

Chan said she was aware that the "price of medicines and other products can be prohibitive, effectively blocking access to care." But, she added, public health needs innovation.

"Resistance develops and drugs fail, creating an urgent need for second- and third-line medicines," she told the meeting in Geneva. "We have seen this problem most acutely with HIV/AIDS. We are seeing it again with the spread of extensively drug-resistant tuberculosis, which is far more costly and difficult to treat."

Under rules agreed by the World Trade Organization, countries can issue so-called "compulsory licenses" to disregard patent rights, but only after negotiating with the patent owners and paying them adequate compensation. If they declare a public health emergency, governments can skip the negotiating.

Brazil and Thailand have invoked the procedure to import cheap generic versions of American AIDS drugs, among other medicines, to treat patients who developed resistance to older anti-retrovirals and needed more expensive, second-line drugs.

The moves by Brazil and Thailand were praised by health campaigners but criticized by industry groups. The United States later placed Thailand on a copyright watch list of nations where American companies face problems protecting intellectual property rights. Countries on the list are under extra scrutiny and can face trade sanctions if alleged violations worsen.

The international aid group Oxfam says compulsory licensing almost never occurs because developing countries face pressure from rich governments acting on behalf of their drug companies. Its report last year on drug access cited WHO statistics that 74 per cent of AIDS medicines are still under monopoly, and that 77 per cent of Africans still lack any access to AIDS treatment.