Trade ministers from the United States and 11 other countries have opened talks in an attempt to meet a US deadline to forge a trans-Pacific trade pact before the end of the year.
However, analysts said an agreement on the proposed Trans-Pacific Partnership (TPP) was unlikely to be reached during the four-day meeting and activists slammed the US for manipulative tactics in a bid to get a deal done.
The TPP is being negotiated by 12 nations - Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the United States and Vietnam. Together they make up 40 per cent of the global economy.
Washington has spearheaded the secretive talks, which have been denounced by non-government groups for their alleged lack of transparency.
The ministers, who arrived in Singapore from the just-concluded World Trade Organisation talks in Bali, did not issue any statement as they began the meeting.
President Barack Obama has hailed the TPP as a centrepiece of renewed US engagement in Asia, saying it contains market-opening commitments that go well beyond those made in other free-trade accords.
But the complexity of issues relating to the partnership has already caused negotiators to miss the original 2012 deadline set by Obama to reach a deal, with the new target also looking unlikely.
"They aren't very far away from a deal but my own guess is that they are more likely to conclude around March," said Deborah Elms, a specialist on the TPP at the Sinnathamby Rajaratnam School of International Studies (RSIS) in Singapore.
The year-end deadline had "looked problematic for months" and differences remained, she said.
However there was a "very slim chance" the ministers might announce a "political agreement", she said.
"This means that they take the photographs in Singapore... and announce a deal and then finish up the hard parts later," said Elms, head of the Temasek Foundation Centre for Trade and Negotiations at RSIS.
"But this strategy seems a bit risky to me, as it means that they really have to sort out the last remaining tough spots and do it rather hastily afterwards."
US Vice President Joe Biden, who is in South Korea on the final leg of a Northeast Asia tour, said more work needed to be done to secure a deal before the year-end deadline.
"We have to end the bureaucratic hurdles that close off trading in key sector trading like autos and agriculture," said Biden, who also welcomed South Korea's interest in joining the TPP talks.
"We have to agree on final regulations that allow financial institutions to operate fully."
While in Japan on Tuesday, Biden pushed Tokyo to step up efforts to open its car and farm markets.
Foreign car manufacturers have long complained that Japanese authorities erect huge barriers to the country's lucrative market and Tokyo has insisted it will never lift all tariffs on sensitive farm products amid strong domestic opposition to opening up the sector.
TPP negotiators have also been divided over patent issues, in particular on medicines.
