The World Trade Organization diplomats have failed to reach final agreement on a deal to allow poor countries to import cheap copies of patented drugs for killer diseases like HIV/AIDS, malaria and tuberculosis. The failure was a big surprise as the same officials had earlier accepted the agreement after the U.S. ended an eight-month holdout and agreed to the deal.

"Following many hours of intensive consultation, there is a problem with respect to the interpretation," said WTO spokesman Keith Rockwell following the adjournment of the meeting at 1 a.m.

Although another meeting is still possible later Friday, Rockwell said it was now "very unlikely" that a decision could be taken before a meeting of trade ministers from the WTO's 146 member countries in Cancun, Mexico, opening Sept. 10.

The WTO's intellectual property panel earlier adopted a document first proposed last December that will let developing countries ignore some patent rules in importing drugs from cheaper generic manufacturers, along with a statement that aimed to calm the fears of U.S. drug companies.

However when the WTO then immediately called a meeting of the body's general council, which has to give the final approval, differences began to emerge. Despite hours of closed-doors negotiating, agreement proved impossible.

Under WTO rules, countries facing public health crises have the right to override patents on vital drugs and order copies from cheaper, generic suppliers. However, until now they could only order from domestic producers -- useless for the huge majority of developing countries that have no domestic pharmaceutical industry.

U.S. pharmaceutical research companies were concerned that a deal to allow countries to import generic drugs would be abused by generics manufacturers and could also lead to drugs being smuggled back into rich countries.

To satisfy those concerns, the document was accompanied by the new statement setting out conditions for the use of the measure.

The statement says that rules allowing countries to override patents "should be used in good faith to protect public health ... not be an instrument to pursue industrial or commercial policy objectives."

It calls for special measures to prevent drugs being smuggled back to rich country markets, including special packaging or different colored tablets. Developed countries would agree not to make use of the provision. Some of the wealthiest developing nations would only use the measure in "situations of national emergency or other circumstances of extreme urgency," it added.

Diplomats earlier had congratulated themselves on what they believed was a deal. This failure likely will throw a huge cloud over the Cancun meeting and could jeopardize the chance of delegates reaching agreement on other issues as part of the current "round" of trade liberalization negotiations.