By Susan Heavey

WASHINGTON (Reuters) - U.S. President Donald Trump on Wednesday signaled a new direction in U.S.-China trade talks and said any deal would need "a different structure," fueling uncertainty over current negotiations and sending U.S. stocks lower.

In an early morning post on Twitter, Trump said the current track appeared "too hard to get done" and cited difficulties such as verification, but he gave no other details about what he or his administration was looking for amid ongoing negotiations.

Representatives for the White House did not respond to a request for more information about the president's statement.

Representatives for China's Foreign Ministry did not immediately respond to a request for comment on Trump's statement.

"Our trade deal with China is moving along nicely, but in the end we will probably have to use a different structure in that this will be too hard to get done and to verify results after completion," Trump wrote in his post.

U.S. stocks slipped after his comments, with all three major indexes down less than 1 percent in late morning trading as analysts anticipated a rocky session.

Trump's statement comes amid the negotiations between the world's two largest economies after potential tariffs on both sides raised fears of a trade war, even as some tensions have eased over signs of some possible progress.

Both sides claimed victory on Monday and pledged to continue talking after last week's round in Washington produced pledges that China would import more American energy and agricultural commodities, although there were no specifics.

U.S. Commerce Secretary Wilbur Ross was expected to visit China next week to help finalize an agreement. U.S. Treasury Secretary Steven Mnuchin told CNBC on Monday that Ross aimed to negotiate "a framework" that could then turn into "binding agreements ... between companies."

Trump on Tuesday, however, told reporters he was not pleased with recent talks, calling them "a start."

Any firm deal is likely to take a long time, according to most observers, and U.S. officials have threatened to return to tariffs, which prompted the current standoff, if needed.

Trump initially threatened to impose $50 billion in tariffs on Chinese goods, prompting Beijing to retaliate with a levy on U.S. products, particularly agricultural goods. Trump then responded by threatening another $150 billion in tariffs.

Trade talks have also been clouded by separate negotiations over the nuclear weapons program in North Korea, which counts China as its sole major ally.

Trump is seeking to win a major deal with Pyongyang to denuclearize and is eyeing a June 12 summit with North Korean leader Kim Jong Un. On Tuesday, however, Trump raised doubts the meeting would take place as planned, and suggested Kim’s recent meetings with Chinese President Xi Jinping had influenced Kim to harden his stance.

(Reporting by Susan Heavey in Washington; additional reporting by Ben Blanchard and Ryan Woo in Beijing; editing by Nick Zieminski and Jonathan Oatis)