HIROSHIMA, Japan — When Korea was still a colony, Park Boo's parents were forced to leave their homes and families behind and come to Japan to work in Hiroshima. Soon after, they endured an unimaginable trial — the world's first atomic bomb attack.

"They were here when the city was bombed," Park said. "Miraculously, they both survived."

But more than 20,000 other Koreans were not so lucky.

On the eve of Hiroshima's main commemoration, expected to draw more than 50,000 people on Saturday, a small crowd of Koreans gathered in Peace Memorial Park Friday to offer prayers and flowers to compatriots killed when the United States dropped the atomic bomb here on Aug. 6, 1945.

Roughly 140,000 people died within a few months of the blast. Another 80,000 were killed when a second bomb was dropped on Nagasaki on Aug. 9. Japan surrendered on Aug. 15, 1945, bringing World War II to an end.

The tragedy of the Koreans was long ignored, and no one knows for sure how many died here.

"Many Koreans were sent back to Korea soon after the war ended and Japan was no longer the colonial ruler," said Park, who helped organize the gathering on Friday. "Nobody here cared about the Koreans who were killed. They were just forgotten and ignored."

Estimates of the death toll are based on the overall number of Koreans known to have been in Hiroshima at the time. They made up about 10 percent of the total population, then about 350,000. Because the city recognizes 260,000 bomb-related deaths over the years, Koreans believe their toll was more than 20,000.

Though the Korean victims are now eligible for medical benefits and have their own monument in peace park, many of their compatriots say they have not yet received proper recognition for the suffering they were forced to endure.

"I don't think the Japanese have ever sincerely apologized for the war and the suffering it caused, including in Hiroshima," said Yi Jae-yong, a 29-year-old peace activist from Taegu, South Korea.

"What happened was terrible," said Kim Bong-seon, another organizer.

The Korean gathering was one of many memorials, most of them small and quiet, in Peace Memorial Park on Friday.

Takaomi Tahara, who helped organize a memorial for construction workers who were killed, said he just hopes Hiroshima's message gets out.

"I have mixed feelings about why Hiroshima was bombed, and about what Japan did during the war," he said. "But once every year, I think it is good for our city to be the world's Mecca of peace."