The US State Department is disappointed at a decision by the Australian government to block a $A3.4 billion takeover of GrainCorp by Archer Daniels Midland.
Treasurer Joe Hockey on Friday said he did not believe a 100% take-over would be in the national interest.
"We are disappointed by the government of Australia's decision," a State Department spokeswoman told the Australian Financial Review on Monday.
The US was the largest foreign direct investor in Australia, with $US132 billion (A$145 billion) in investment projects to date, it said.
"We look forward to working closely with Australia's government to build stronger trade and investment ties."
"This was a very complex case," parliamentary secretary Josh Frydenberg told Sky News, citing GrainCorp's dominant position over east coast bulk grain exports.
"It was never going to be easy to make a decision."
The ABC reports shares in GrainCorp closed at $A8.72 on Friday, down 22%, or $A2.48, following the announcement.
ADM already owns around 20% of GrainCorp. The BBC reports its bid to fully acquire the company was opposed by some farm groups, who raised concerns over the impact of such a move on competition in the sector.
Resignation of chief executive
GrainCorp chief executive Alison Watkins has resigned.
In a statement on Monday, Ms Watkins said she had intended to leave the company after the planned takeover by ADM, but Mr Hockey's decision to reject the move forced a change of plan.
"I have carefully weighed my options over the past two days," Ms Watkins said.
"Given last week's unexpected developments, I feel it is in the best interests of GrainCorp, our people and customers that I move on now and allow the board to find new leadership to take the business forward into its new phase," she said.
GrainCorp said Ms Watkins will leave the business in mid January to become managing director of Coca-Cola Amatil.
AAP reports chairman Don Taylor temporarily will take on the role of executive chairman and will be appointed acting chief executive following Ms Watkins departure, while the company looks for a permanent replacement.
