WTO countries looked set Thursday to clinch a deal here to solve a longstanding problem over access to cheap drugs for poor countries to fight diseases such as AIDS and malaria after the US dropped its opposition in return for assurances for its pharmaceutical producers.

Washington and key developing countries agreed a draft proposal on Wednesday, marking a breakthrough in the issue that has overshadowed global trade talks since 2001.

The proposed solution is to go before the rest of the World Trade Organisation's 141 members for approval later on Thursday, but most have already signalled informally they would endorse the deal, trade sources said.

"It's not a done deal but it's close," one trade source added.

Several countries have raised questions over the legal status of the proposed solution -- in the form of a so-called chairman's statement -- and whether it would be legally binding, the source said.

Trade envoys had been keen to resolve the issue at a meeting this week of the ruling general council in a bid to boost a ministerial gathering in the Mexican resort of Cancun in two weeks.

The September 10-14 conference aims to take decisions in key areas such as agriculture, industrial products and trade in services amid efforts to kickstart the flagging Doha trade negotiations.

The deal proposes the relaxing of global patent rules to enable poor countries without a pharmaceutical industry to import cheaper generic copies of patented essential medicines.

The proposed solution, which follows weeks of intensive consultations, aims to quell US fears over an accord backed by all the WTO's membership except Washington last December.

Under pressure from its pharmaceutical industry, the US blocked the deal because of concerns that it could be interpreted to include products for non-infectious diseases such as obesity or impotence.

Faizal Ismail, the South African representative at the talks, said the proposal aimed to help provide "some comfort" to the pharmaceutical industry.

"Their concern was about potential abuse of this arrangement and the possibility that it would not be used in good faith," he told reporters on Wednesday.

"In my view this statement meets that criteria."

The deal struck Wednesday by the US, Brazil, India, Kenya and South Africa would be in the form of a statement read by the chairman of the WTO general council to accompany the December text.

It states that the new rules would be used "in good faith" to protect public health and not for commericial or industrial objectives.

It also stresses the importance of ensuring that generic medicines are not diverted back to rich country markets, and that 23 developed countries would not use the solution to import generic drugs.

The 10 leading candidate members of the European Union would also opt out unless faced with emergencies until they become full members of the bloc next year.

And a group of middle-income developing countries is also expected to agree to opt out from using the solution unless faced with a national emergency.

But the international aid agency Oxfam criticised the proposed deal, saying it was flawed and unworkable.

"It is profoundly unfair to create fresh legal obstacles for developing countries trying to obtain affordable generic medicines, purely in the interests of an industry that in the US alone made 37 billion dollars (34 billion euros) in profit last year," Oxfam representative Celine Charveriat said in a statement.