For a moment, the US's unease about how to respond to the recent violence in Xinjiang was there for all to see. Barack Obama, the president, was visibly discomfited this week when, during his joint press conference with Dmitry Medvedev, his Russian counterpart, he was asked to comment on the riots and on China's subsequent crackdown.
Mr Obama avoided making any remark, pointing out that he had been “travelling all night and in meetings all day”, was not fully briefed and that the US would instead release an official statement.
The issue is a classic test of Washington's readiness to take a stand on what China labels as its internal affairs and what human rights activists say is a question of global concern.