execution of Son Jong Nam, a Christian who expressed concern over the situation in his Communist-run nation, organizers said.
A protestor was bound to a tree outside the Embassy with three strips of cloth, in imitation of a North Korean execution, said UK-based advocacy group Christian Solidarity Worldwide (CSW) which co-organized the rally.
"His head was shrouded in a symbolically blood-stained cloth, giving a striking representation of the effect of the bullets typically fired by three marksmen at the head, chest and stomach of victims of execution in North Korea," CSW told BosNewsLife.
Protestors wearing gags also observed a minute’s silence for 48-year old Son Jong Nam. Songs were led by the internationally-known artist Graham Kendrick, while prayers and chants were made in English and Korean during the peaceful protest.
A letter expressing concern over Son's situation was read over the microphone to the crowd and later delivered via the Embassy’s postbox.
"We are deeply concerned that the treatment of Mr Son and his lack of access to the judicial process are in grave violation of international standards that are binding on the Democratic People’s Republic of Korea," the letter said.
"We cannot accept that a nation which has diplomatic privileges in our nation should blatantly violate its international obligations. We urge you to take immediate and effective steps to ensure international law is respected and that the breaches of these laws in the case of Mr Son are remedied as a matter of urgency."
Another protest for Son was held Friday, April 28 in South Korea where 24 organizations urged the National Human Rights Commission support international intervention to save the life of Son Jong Nam.
The demonstrations coincided with North Korea Freedom Day when groups are tackling reported human rights violations taking place in North Korea with at least one rally planned in Washington DC.
"It is imperative we lift our voices to protect the life of Mr Son. We are deeply concerned about his plight and the horrors the North Korean regime are perpetrating against him," said CSW National Director Stuart Windsor. "We hope that the North Koreans will take note of the concern that exists around the world and will cease their practice of torture and execution of innocent people."
Son's case has come to symbolize the plight of thousands of Christians and dissidents in prisons and labor camps throughout North Korea, human rights groups suggested. Christian rights groups Open Doors has put North Korea on top of its World Watch List of 50 countries with severe persecution of Christians.
The North Korean government denies human rights abuses.
Christians often suffer as North Korea's Stalinist system is based on total devotion of the individual to an ideology promoted by the late leader Kim Il Sung and his successor and son, Kim Jong Il, observers who recently visited the country said.
The ideology largely resembles a religion or cult, and refugees' accounts say those who oppose it are dealt with severely, often ending up in prison camps. Despite the risks there are believed to be likely tens of thousands of practicing Christians.
Kim Il Sung, the man recruited in 1945 by Soviet leader Joseph Stalin to found the Communist North Korean state, stamped out Christianity and the traditional Buddhism and Shamanism.
His ideology, which preaches self-reliance, is known as Juche, of which the late Kim is the central figure - so much so that the North Korean calendar begins with the year of his birth in 1912. One of the tallest structures in Pyongyang is the Juche Tower, built in Juche 70, or 1982.(With reports from North Korea and London).