U.S. national security adviser Jake Sullivan sat down with China’s top diplomat for two days of what the White House called "substantive and constructive” meetings, a sign that the sides are working to ease strains that led to a breakdown in even the most routine communication.

Sullivan’s May 10 to 11 meetings in Vienna with Wang Yi touched on "key issues in the U.S.-China bilateral relationship, global and regional security issues, Russia’s war against Ukraine, and cross-Strait issues, among other topics,” the White House said in a statement.

The talks lasted for more than eight hours over the two-day session, with Sullivan reiterating U.S. concerns about China potentially offering lethal aid to Russia amid its invasion of Ukraine and focusing on how to manage tensions over Taiwan, a senior administration official told reporters Thursday.