Terry Branstad, the U.S. envoy to China, is stepping down and returning home by early October - a resignation that comes as political and diplomatic ties between the two countries worsen, Secretary of State Mike Pompeo says.

On Twitter, Pompeo thanked Branstad for his contribution to rebalancing China-U.S. ties "so that it's results-oriented, reciprocal and fair." Pompeo confirmed Branstad's departure to U.S. President Donald Trump by telephone, a statement from the consular office in Beijing said.

China-U.S. ties have soured over many matters - including U.S. denunciation of China's security legislation in Hong Kong to its handling of COVID-19 and its aggressive stance in the South China Sea.

There was no immediate statement that a revamp was being initiated following the ambassador's resignation. There was no mention of whom Trump would pick as Branstad's successor.

He will return to Iowa, where Branstad served as governor for six terms - and where Trump got many votes to win the 2016 presidential election. The 73-year-old Branstad had served as a diplomat in China since May 2017.

Trump suggested last week that Branstad might be participating in the electoral campaign. In a Twitter video by Iowa Sen. Joni Ernst, the president said Branstad would be leaving Beijing "because he wants to campaign," the Los Angeles Times reported.

According to Pompeo, Trump selected Branstad because his more than 10 years of experience dealing with China made him an ideal person for the position and to defend U.S. interests in this critical relationship.

China's Ministry of Foreign Affairs acknowledged Pompeo's social-media comments but said it was yet to receive official notice of Branstad's departure.

Branstad's resignation leaves the U.S. consulate in Beijing without a representative. The post might remain vacant for months - even if Trump wins the Nov. 3 election.