President Donald Trump has cast doubt on the prospects for talks that are designed to head off a trade war between the United States and China.

Key points: Donald Trump says negotiations require new structure to allow America to "verify results"

Donald Trump says negotiations require new structure to allow America to "verify results" Commerce Secretary Wilbur Ross will soon travel to Beijing to try to settle the details

Commerce Secretary Wilbur Ross will soon travel to Beijing to try to settle the details China's Commerce Ministry pledges to work "conscientiously" with Washington

Four days after the two countries suspended plans to impose tariffs on up to $US200 billion ($265 billion) worth of each other's goods, Mr Trump declared in a tweet that a more detailed agreement "will be too hard to get done".

While saying the talks were "moving along nicely," Mr Trump said negotiations with China would require "a different structure" and would need to allow America to "verify results after completion".

It was unclear what kind of structure the President had in mind.

After high-level talks last week in Washington, Beijing agreed in a joint statement with the US to "substantially reduce" America's trade deficit with China. But it failed to commit to shrink that deficit by any specific amount.

The Trump administration had sought to slash the gap by $US200 billion.

And the statement said little of the key dividing issue between Washington and Beijing: The methods China uses to try to overtake US technological supremacy — from cyber theft to its demands that American companies hand over some of their technology in exchange for access to the Chinese market.

Still, Treasury Secretary Steven Mnuchin said China had agreed to dramatically increase purchases of US farm and energy products.

And on Monday, Mr Trump had hailed the cease-fire as a big victory for US farmers.

Commerce Secretary Wilbur Ross will soon travel to Beijing to try to settle the details.

But the agreement — which contained no specifics — drew fire from those who had supported Mr Trump's campaign pledge to crack down on what they call China's abusive commercial trade practices.

Dan DiMicco, a former steel executive who advised Mr Trump during the 2016 presidential campaign, dismissed the truce as "more false promises and delaying tactics".

Mr Trump's tweet on Wednesday (local time) suggested the President was now feeling more doubtful about the talks with China.

"It's hard to tell if this is the result of strategy or just a reaction to the latest criticism he's felt," said Scott Kennedy, director of the Project on Chinese Business and Political Economy at the Centre for Strategic and International Studies.

Washington demanded China reduce its trade surplus by $US200 billion ($266 billion) during initial talks in Beijing. ( Reuters: File )

In Beijing, the Commerce Ministry pledged on Wednesday to work "conscientiously" with Washington ahead of Mr Ross's visit. But it gave no details of any new initiatives.

Last month, the administration proposed tariffs on $US50 billion ($66 billion) on Chinese imports to protest the forced technology transfers.

Mr Trump later ordered Robert Lighthizer to seek up to an additional $US100 billion ($133 billion) in Chinese products to tax.

China responded by targeting $US50 billion in US products, including soybeans, which would deal a blow to Mr Trump supporters in America's heartland.

The prospect of an escalating trade war has shaken financial markets and alarmed business leaders.

AP