BEIJING — A 13-year-old American boy campaigning to turn the demilitarized zone between North and South Korea into a peace park has been taken away by Chinese police after staging a brief protest near Tiananmen Square.

Jonathan Lee unfurled a sign saying "peace treaty" and "nuclear free DMZ children's peace forest" as he stood outside the Forbidden City on Monday.

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.

Lee, of Ridgeland, Mississippi, made a rare visit to Pyongyang in August to propose his idea of a "children's peace forest" in the demilitarized zone.

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The 2 1/2 mile-wide DMZ is the most heavily guarded border in the world, sealed off with electric fences and studded with land mines, watchtowers and military bases.

Impoverished North Korea is one of the most isolated countries in the world and its hard-line communist regime is under United Nations sanctions for launching missiles and refusing to comply with nuclear weapons inspections.

Since the 1950-53 Korean War ended with a cease-fire and not an armistice, the United States, South Korea and North Korea remain technically at war.