Minutes into a more than two-hour show Sunday night, John told the audience that the performance was dedicated “to the spirit and talent of Ai Weiwei,” according to several audience members. They said the crowd rumbled in recognition that Ai remains a touchy subject for the Chinese government.

An internationally acclaimed sculptor and installation artist, Ai has used his art and his renown to draw attention to social injustice. He was detained for nearly three months last year, and he remains barred from leaving China.

Ai and John met each other briefly on Sunday before the concert. “I super like him,” Ai said on his feed on Twitter, which is banned in China but on which he has 180,000 followers.

China-based online media sites reported on John’s Beijing show, as they did on a Friday night performance in Shanghai, but they did not report John’s remark about Ai.

The Chinese government exercises tight control of live performances, requiring artists to submit detailed lists of songs, casts and crew members before approval is given. Censors further tightened scrutiny after singer Bjork shouted “Tibet, Tibet” at the close of a song titled “Declare Independence” at a Shanghai performance in 2008.