The United States is set to send Michael Chase, the deputy assistant secretary of defence for China, Taiwan and Mongolia, to China's top annual security forum in mid-September, a U.S. official has told Reuters.

The choice of Chase was not previously reported. He is more senior than the U.S. official who attended the Xiangshan Forum last year, but his rank is in line with historical norms for the Pentagon.

Deputy Assistant Secretary of Defense for China Chad Sbragia attended the forum in 2019.

There is some hope that this could signal deeper working-level engagement with China amid regional disputes. The official, who spoke on condition of anonymity, said Chase's expected attendance was not unprecedented but sent a message that the United States prioritises engagement at the military level with China even at a time of heightened tensions.

More than 90 countries and international organisations plan to send delegations to the Sept. 12-14 forum in Beijing, Chinese state media reported Wednesday.

Washington sent Xanthi Carras, China country director in the Office of the Undersecretary of Defense, when the forum resumed last year after a three-year hiatus due to the pandemic. It was a sign of thawing military ties; however Carras' title is of a lower rank than Chase or Sbragia.

Chase co-chaired U.S.-China military talks in Washington in January - the first such working-level talks since 2022, when most bilateral military engagement was suspended after then-U.S. Speaker Nancy Pelosi's visit to Taiwan.

Taiwan and the South China Sea remain contentious flashpoints in the U.S.-China relationship, with both sides unwilling to compromise on "core issues". U.S. National Security Adviser Jake Sullivan said no new agreements had been reached on the South China Sea during a visit to China last week.

China has repeatedly criticised U.S. deployments in the Asia-Pacific region, including the placement of long-range missiles in the Philippines, as well as U.S. arms sales to democratically governed Taiwan, which China considers its own territory, over the strenuous objections of Taipei.

Meanwhile, the U.S. has raised concerns over China's "aggressive" actions in the South China Sea, its frequent military manoeuvres in the air and waters surrounding Taiwan, and what it says is the opacity of China's nuclear buildup.

Official nuclear talks were halted by Beijing in July in protest over U.S. arms sales to Taiwan. But both sides have agreed that U.S. Indo-Pacific Command leaders would soon speak by phone to their counterparts in China's southern theatre command, which covers its southern seas.

(Reporting by Idrees Ali and Laurie Chen in Beijing; Writing by Laurie Chen. Editing by Gerry Doyle and Raju Gopalakrishnan)