A 13-year-old US boy, who is campaigning to turn the demilitarised zone (DMZ) between North and South Korea into a peace park, was released from Chinese detention on Monday along with his mother, after staging a brief protest near Tiananmen Square in Beijing.
Jonathan Lee unfurled a sign saying "peace treaty" and "nuclear free DMZ children's peace forest" as he stood outside the Forbidden City earlier in the day.
A man presumed to be a plainclothes officer grabbed Lee's sign less than a minute later, and waved away journalists who had been contacted by Lee's family ahead of time.
Lee and his mother were escorted away by police, and held for a few hours.
Later Lee and his mother, Melissa Lee, returned to their hotel, the Courtyard Marriott.
Then they, and the boy's father and sister, checked out of their rooms, a hotel receptionist said.
The family were later seen at Beijing Airport, boarding a flight to Seoul.
Joel Clark, a documentary filmmaker who travelled to China with the Lees, said an email he received from Mrs Lee suggested that they had been told to leave China.
Lee made a rare visit to Pyongyang, North Korea, in August to propose his idea of a "children's peace forest" in the demilitarised zone.