Deadlocked negotiations for a global trade treaty are threatening the credibility of the World Trade Organization, the U.S. ambassador to the trade body said.

Negotiators meeting to discuss the long-stalled Doha round moved no closer to agreeing even a scaled-back treaty that would focus on the needs of poor states, agreeing only to keep negotiating for another month and then consider their options.

"What's at risk is the WTO being seen as an effective forum for negotiating trade liberalisation," U.S. ambassador Michael Punke said in a telephone interview following a morning of deliberations at the WTO.

Ten years of negotiations in the 153-member WTO have failed to seal an accord that could generate billions of dollars and alleviate poverty by freeing up trade in goods and services.

A stop-gap deal proposed by WTO chief Pascal Lamy last month required that rich countries make good on promises made in 2005 to trim cotton subsidies, import most goods duty-free from least-developed countries and simplify sourcing rules for exporters in poor countries.

Originally that stop-gap was to take effect while negotiators try and address more divisive market-opening issues.

But trading countries led by the United States want to expand the slimmed-down agreement in a way that will distribute the burden of commitments to poor states.

A potential expanded agreement could include issues from a reform of fisheries subsidies to tariff cuts for environmental goods and harmonisation of border controls -- sensitive issues whose inclusion further trims chances of agreement by the time trade ministers gather in Geneva in December.

An idea floated by the European Union to freeze tariffs while negotiations continue was welcomed by the United States and Australia during Wednesday's meeting, but opposed by developing countries such as India and Brazil.

Negotiators agreed they should assess chances of forging a December agreement by late July, and if necessary postpone that deadline again.

"It is also very clear .. that we need to consider the (post-December) work on (Doha)," Lamy told negotiators. (Reuters)