Sun Wenguang said he had been trying to pay his respects to the late communist leader Zhao Ziyang, who was purged for supporting the 1989 Tiananmen protests.

Mr Sun, 75, had visited Mr Zhao's grave annually, but this year marks the 20th anniversary of the Tiananmen crackdown.

The Chinese government treats its crushing of pro-democracy protests on Tiananmen Square as taboo.