Announcing the talks at the World Trade Organisation had been suspended, Indian Trade Minister Kamal Nath said it could take “from months to years” to restart the negotiations.
"This is a serious setback, a major setback," said Celso Amorim, the Brazilian foreign minister.
The complex talks were launched in Doha, Qatar, five-years ago in a drive and described as a "once-in-a-generation chance" to boost the global economy and lift millions out of poverty worldwide.
But the Doha round stalled after 14 hours of talks between the G6 members - the US, EU, Brazil, Australia, Japan and India - yielded no breakthrough in reducing farm subsidies and lowering agricultural tariffs.
Peter Mandelson, the EU trade commissioner, told journalists that Washington had been "unwilling to accept or indeed to acknowledge the flexibility shown by others."
Christine Lagarde, the French trade minister, blamed "intransigence" by the US for the dead end.
Peter Mandelson said the US was
not being flexible
But the US said the EU and other "protectionist" WTO members had not lowered farm tariff barriers enough to allow it to move further on subsidies.
France believes countries should now seek regional trade negotiations as a way around the impasse.
Washington has said its offer to reduce farm subsidy limits by 60 per cent was significant, but trade rivals argued the cuts left real spending unaffected.
Diplomats said Mandelson had spelt out how close Brussels could get to the level of tariff and subsidy cuts demanded by developing countries, but that was not enough for the US.
Ahead of the talks Pascal Lamy, the WTO director general, had said the US must offer deeper cuts in its farm subsidies, the EU must further drop barriers to farm goods' imports and the big developing countries must agree to open up their markets for industrial goods.
Despite the failure of the talks, all G6 members say they remain committed to the multilateral trading system and to the eventual completion of the Doha round, even if they could not say how or when the negotiations could be revived.
The process is running out of time as the authority of George W. Bush, the US president, to "fast track" the trade deal - which allows the White House to make deals that can be either approved or rejected by Congress, but not amended - runs out in mid-2007.
The G6 countries account for some three quarters of world trade and consequently represent a wide range of commercial interests.