Australia is in the box seat to crack the US sugar market, leaked trade documents show. But, in return, it may have to allow US companies to sue Australian governments in international tribunals, a concession it has not been willing to make until now.

The leaked documents published by The Huffington Post and WikiLeaks are a memo and spreadsheet prepared by negotiators from one of the 12 nations attempting to reach agreement on a so-called ''Trans-Pacific Partnership'' encompassing Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, the US and Vietnam - nations that, between them, account for 40 per cent of the world's gross domestic product.

The memo portrays the Australian delegation, led by Trade Minister Andrew Robb, as resisting attempts by the US to increase the influence of drug manufacturers over the Pharmaceutical Benefits Scheme.

Australia is not prepared ''to go beyond'' the conditions it has already agreed to in its free-trade agreement with the US, it says.

But Australia has begun working behind the scenes with the US and Japan to reintroduce rejected clauses that would give US drug firms greater influence over the decisions of other nations.

''The Australian position is unclear and begins to show some weakness,'' the memo says.

The leaked document, prepared after the first day of the five-day ministerial talks in Singapore, says the US is exerting ''great pressure'', which is expected to increase.

One of the US techniques is to set up smaller groups of nations that formulate agreed positions known as ''landing zones'' that tend to show ''a solution coming from the US position''.

It is ''critical for other countries to reinsert their positions to avoid losing their positions in a text that can be used by the United States later to try to reach agreement'', it says.

A draft intellectual property chapter published by WikiLeaks and Fairfax Media last month detailed US proposals to make the citizens of other nations pay more for movies and software and be placed under surveillance as part of a crackdown on internet piracy.

On many of those questions Australia had sided with the US and was sometimes the only nation to have done so.

Finance Minister Mathias Cormann has refused a request from the Australian Senate to see the text of the agreement before it is signed.

Under Labor, the Australian government flatly refused to sign any agreement that let foreigners sue it overseas. But Mr Robb has indicated he is prepared to consider such procedures in return for ''substantial market access'' - namely sugar.

Leaked Memo Reveals 'Weakness' In Trans-Pacific Partnership Delegation's Trade Stance