Organizers said the rally is aimed at calling for greater global attention to the plight of North Koreans on the 20th anniversary of the fall of the Berlin Wall.

About two dozen participants called for ending all political prisons in North Korea and bringing authoritarian leader Kim Jong Il to justice during the demonstration at the South Korean border town of Imjingak.

They also sent thousands of leaflets condemning the regime in Pyongyang aboard a balloon that flew across the border.

"It's a crime if we keep silent" on North Korea's human rights abuses, said Kang Min-hee, an organizer. "Siberian gulags are gone. So are the Chinese ones. But gulags still remain in North Korea."

The totalitarian regime is estimated to be holding some 154,000 political prisoners in six large camps across the country, South Korean lawmaker Yoon Sang-hyun said in a statement last month, citing government data.

Offenses meriting banishment to a prison camp include everything from disparaging leader Kim Jong Il to trying to flee the country, defectors and prison survivors have said.

Prisoners are forced to toil for more than 10 hours a day, are fed a poor diet and do not receive medical aid. They are also banned from communicating with their families while in prison, according to the statement.

Pyongyang rejects outside criticism on its alleged human rights abuses and the existence of gulags, denouncing it as part of a U.S. attempt to overthrow its regime.

In April, the North revised its constitution to say the state "respects and protects" human rights for the first time in a move seen by analysts as aimed at fending off international criticism about its harsh treatment of citizens.

Korea was divided into the North and the South right after its liberation from Japan's 1910-45 colonial rule.

The two sides still remain in a state of conflict as the 1950-53 Korean War ended in a truce, not a peace treaty.

The Berlin Wall, the symbol of Germany's division into east and west after the country's defeat in World War II, came down on Nov. 9, 1989, heralding the unification of the two former states the following year.