Speaking from Geneva after a teleconference meeting with the trade chiefs of Brazil, India, Australia and the EU, Portman said the EU's latest offer on agricultural trade did not go far enough.

"We are a little discouraged today by the EU proposal. I believe it is a modest step in the right direction but I believe it's inadequate to meet the promise of Doha," he told US reporters, referring to the WTO round of talks.

"While in some areas the EU proposal moves in the right direction, overall we are disappointed both in the level of the tariff cuts and the exclusions from the tariff cuts," Portman said.

The European Commission earlier Friday offered its steepest-ever cuts in agricultural tariffs to try to break a deadlock in WTO talks ahead of a crucial ministerial meeting in Hong Kong in December.

The EU's executive arm said it would be prepared to cut the 25-nation bloc's highest farm tariffs by 60 percent and the lower tariffs by 35 to 60 percent, almost halving the overall tariff rate from 23.0 percent to 12.0 percent.

Portman said his colleagues from Brazil, India and Australia agreed with him that the EU tariff cuts were insufficient and came with too many strings attached.

EU trade commissioner Peter Mandelson said in Brussels earlier that the offer was "substantial, credible and comprehensive" and warned: "This is Europe's bottom line."

But Portman said: "This is not the time for take-it-or-leave-it proposals."

The US trade chief expressed sympathy for Mandelson and EU farm commissioner Mariann Fischer Boel, who have been accused by France of overreaching their negotiating mandate at the WTO.

"But at the end of the day we need to have a proposal that actually meets the goal of Doha ... which opens up all of our markets more to achieve the economic growth and development objectives," Portman said.

"The ball is in all of our courts, including theirs (the EU's). We have now several proposals on the table. We need to come up with a solution.

"We are very close to the Hong Kong ministerial now so there's no time to waste. We need to bridge this gap," he said.

Portman added that the United States stands "shoulder to shoulder" with the EU in pushing for greater liberalisation in both services and industrial tariffs at the WTO.

But he added: "Whether the EU likes it or not, and whether the United States likes it or not, agriculture is central to this round.

"Unless we can make progress on agriculture, I think as a practical matter it will be impossible to see the progress we both would like to see in these other areas."

Portman said he believed that India and Brazil, which are seen as pivotal players representing the developing bloc of nations at the WTO, were willing to move on services and industrial tariffs if the agriculture talks progress.

"They say it's always darkest before the dawn," he added.