The US House of Representatives has voted to block a measure that would have given President Obama fast-track authority to conclude a trans-Pacific trade accord.

The vote, in which some two thirds of the House opposed the so-called Trade Adjustment Assistance, is regarded by commentators as a huge setback for the president, who was hoping that his fellow Democrats would help him finalise negotiations with 11 Pacific Rim countries on what would be the largest trade agreement ever signed — a massive pact with Japan, Australia, Canada, Chile, Vietnam and others, encompassing some 40% of global commerce.

Leading House Democrat Nancy Pelosi said that the trade pact needs to be revised: “Whatever the deal is with other countries, we want a better deal for American workers.” House Speaker John Boehner has left open the possibility of concluding the trade deal at a later date.