BEIJING — The U.S. ambassador to China will step down early next month, ending a three-year tenure marked by a trade war and increasingly bitter relations between the world’s two largest economies.

Terry Branstad, appointed by President Donald Trump in 2017, confirmed his decision in a phone call with Trump last week, the U.S. Embassy said in a statement Monday. It did not give a reason for his departure.

“I am proudest of our work in getting the phase one trade deal and delivering tangible results for our communities back home,” he was quoted as saying at an embassy staff meeting on Monday.

U.S. Secretary of State Mike Pompeo in an interview late Monday thanked Branstad for his service.

“Over the past years, he’s done yeoman’s work helping us deliver on something that’s a complete change from what any administration has done with respect to the Chinese Communist Party,” Pompeo told Fox News.

Word of Branstad’s departure had leaked out earlier in the day when Pompeo thanked Branstad on Twitter for his service.

“Ambassador Branstad has contributed to rebalancing U.S.-China relations so that it is results-oriented, reciprocal, and fair,” Pompeo wrote in a subsequent tweet.

Branstad became embroiled in a recent controversy when China’s official People’s Daily newspaper rejected an opinion column that he had written.

Pompeo tweeted last week that China’s ruling Communist Party refused to run Branstad’s op-ed while the Chinese ambassador to the United States “is free to publish in any U.S. media outlet.”

Chinese foreign ministry spokesperson Zhao Lijian responded that Branstad’s article was “full of loopholes, seriously inconsistent with facts and wantonly attacks and smears China.”