White House national security adviser Jake Sullivan spoke with China’s top diplomat Wang Yi on Friday, people familiar with the matter said, as the two sides look to ease tensions that have continued to build in recent months.

Sullivan’s previously unreported call took place days before Taiwan’s President Tsai Ing-wen is scheduled to stop in the U.S. en route to Central America, a trip that’s likely to further inflame Beijing’s ire. In a sign of the fraught state of U.S.-China ties, neither side opted to publicize the call between Sullivan and Wang.

Spokespeople for the White House and the Chinese Embassy didn’t immediately respond to requests for comment. The people who confirmed the call asked not to be identified discussing private conversations.