Suzan Johnson Cook, the U.S. ambassador at large for international religious freedom, was scheduled to travel to China on Feb. 8, according to several rights advocates who were invited to brief her ahead of the visit. But as the date drew near, Chinese leaders refused to grant her meetings with government officials. …

They then cited her lack of scheduled meetings as a reason for denying her visa application, according to the advocates and a congressional aide, who were briefed on the situation.

Diplomats in Cook’s position have encountered problems before, but denying a visa to a sitting U.S. ambassador represents one of China’s strongest rebuffs to date, experts say.