Activists accused the United States on Sunday of trying to railroad a new Pacific trade pact with 11 partners as their trade ministers entered a second day of secretive talks.
The meetings, due to end Tuesday, are a last-gasp attempt to meet a year-end US deadline to forge a deal on the Trans-Pacific Partnership (TPP), which would cover 40 percent of the world's economy even though it currently excludes China.
International activists opposed to the TPP -- and corporate lobbyists including those supporting the pact -- have also descended on Singapore to try to push their cases.
"The TPP, which is being negotiated behind closed doors by trade bureaucrats and nearly 600 corporate lobbyists, has provoked political uproar because its text has been kept secret from lawmakers in the countries it covers," global advocacy group Avaaz said in a statement.
"If the deal is finalised, corporations will take on new powers to sue governments over regulations which threaten their future profits," it said.
"Laws designed to protect the public, including access to cheap medicines, bans on logos on cigarette packaging, clear labelling of GM (genetically modified) products, and Internet privacy could be under threat."
Activists said Washington was trying to railroad the talks to meet its self-imposed deadline.
US President Barack Obama has hailed the TPP as the economic centrepiece of its strategic shift towards Asia, calling it a 21st-century agreement covering non-tariff areas such as the environment and labour standards and issues such as intellectual property.
"Nearly all of the politically sensitive issues that have arisen in the secretive, closed-door TPP talks are still unresolved," advocacy group Public Citizen said in a statement.
"So, the Obama administration has resorted to extreme tactics at Singapore to try to wring out a deal," it added.
The advocacy group claimed the US has set up invitation-only "green room" meetings at which decisions on difficult issues can be "worked out".
Melinda St Louis, the group's international campaigns director who arrived in Singapore over the weekend, said the tactic was dividing developing countries at the negotiation table.
Jane Kelsey, a University of Auckland law professor also in Singapore to monitor the talks, said: "This is a very manipulative process because it marginalises those that are potential critics and makes it harder for them to continue rejecting compromised deals."
Rodrigo Contreras, Chile's former chief TPP negotiator who quit in March, said he thought the US wanted to close a deal now with the existing text of the proposed agreement rather than "risk" the talks extending into 2014.
But he told AFP by email from Chile any agreement would not be sustainable unless it represents the interests of all the countries.
Many officials from the other participating countries -- Australia, Japan, New Zealand, Singapore, Malaysia, Chile, Canada, Mexico, Brunei, Vietnam and Peru -- view it not only as an economic but a geopolitical tool.
Japanese Prime Minister Shinzo Abe, in deciding to enter talks, spoke of ensuring Tokyo's role in shaping the future of a region marked by China's rise.
China is involved in talks on a rival free-trade grouping in Asia called the Regional Comprehensive Economic Partnership that excludes the US.