A revised Trans-Pacific Partnership trade agreement would have to be "substantially better" if the US was to join, President Donald Trump says.
A White House spokesman confirmed the president had assigned his top trade advisers, US Trade Representative Robert Lighthizer and his new chief economic adviser, Larry Kudlow, "to take another look at whether or not a better deal could be negotiated."
However, Mr Trump tweeted on Friday he would only join the TPP "if the deal were substantially better than the deal offered to Pres. Obama".
"We already have BILATERAL deals with six of the eleven nations in TPP, and are working to make a deal with the biggest of those nations, Japan, who has hit us hard on trade for years!" he wrote.
Mr Trump last year pulled his country out of the TPP, which includes Australia, because he believed it was unfair to American workers and farmers.
However in January at the World Economic Forum he flagged that the US was prepared to negotiate "mutually beneficial, bilateral trade agreements with all countries" including countries in the TPP.
Australia's Trade Minister Steve Ciobo is due to respond to Mr Trump's decision on Friday afternoon.
Japanese Finance Minister Taro Aso was cautious about the president's decision.
Trump "is a person who could change temperamentally, so he may say something different the next day", Mr Aso said.
Prime Minister Shinzo Abe and Mr Trump are expected to discuss the TPP at their summit meeting next week.
The text of the TPP has been tabled in the Australian parliament and two committees are examining it.
A national interest analysis showed the deal would significantly enhance Australia's economic relationships.
Australian Greens trade spokeswoman Sarah Hanson-Young said reports of Mr Trump taking fresh interest in the deal were bad news.
"Many of the worst features of the first dud deal were put on ice as an attempt to build a new deal out of the rubble. But everything that's on ice gets defrosted if the US comes back to the table," she said.
She said longer monopoly rights on medicines would punish Australians suffering from conditions like cancer or rheumatoid arthritis by making medicine more expensive.