WASHINGTON (AP) — President Donald Trump cast doubt Wednesday on the prospects for talks that are designed to head off a trade war between the United States and China.

Four days after the two countries suspended plans to impose tariffs on up to $200 billion worth of each other's goods, 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," 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 U.S. 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 $200 billion.

And the statement said little of the key dividing issue between Washington and Beijing: The methods China uses to try to overtake U.S. 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 U.S. farm and energy products. And on Monday, Trump had hailed the cease-fire as a big victory for U.S. 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 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 Trump during the 2016 presidential campaign, dismissed the truce as "more false promises and delaying tactics."

Trump's tweet Wednesday suggested that 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 Center for Strategic and International Studies.

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

Last month, the administration proposed tariffs on $50 billion of Chinese imports to protest the forced technology transfers. Trump later ordered Lighthizer to seek up to an additional $100 billion in Chinese products to tax.

China responded by targeting $50 billion in U.S. products, including soybeans, which would deal a blow to Trump supporters in America's heartland. The prospect of an escalating trade war has shaken financial markets and alarmed business leaders.