President Trump spoke to China’s top leader, Xi Jinping, on Thursday for the first time since taking office, according to Chinese state media, as a fragile détente in a trade war between the world’s two largest economies shows signs of unraveling.

The call was reported by Chinese state media in a brief dispatch late Thursday that did not immediately include details.

The call comes as tensions between China and the United States have ratcheted up again nearly a month after the two sides met in Geneva and agreed to a pause in the trade war.

On Wednesday, Mr. Trump wrote on social media that Mr. Xi was “VERY TOUGH, AND EXTREMELY HARD TO MAKE A DEAL WITH.”

The Trump administration has accused Beijing of breaking the truce by restricting exports of critical rare earth minerals used by a range of American manufacturers, including carmakers and semiconductor producers. Shortages of the minerals, which are used to make powerful industrial magnets, could bring some American factories to a standstill. China dominates the global market for the minerals and views it as a choke point to lord over the United States.

In response, the Trump administration has proposed a plan to revoke visas for some Chinese students and suspended some sales to China of components and software used in jet engines and semiconductors.

China has denied breaking the terms of the Geneva deal and has accused the United States of escalating tensions.

The White House did not immediately respond to requests for comment.