An American missionary believed to be detained when he stepped into North Korea on Christmas didn't inform his parents of his plans but they had a hunch he would visit the communist nation.

"We had a sense," Pyong Park, the missionary's father, told The Associated Press late Sunday. "We told him to continue what you're doing in South Korea."

About 100 people held candles Sunday night at Palomar Korean Church in San Marcos, a north San Diego suburb, to commend Park for going to North Korea.

"Robert is doing what God called on him to do," the Rev. Madison Shockley told the crowd. "We call this speaking truth to power."

Robert Park, 28, slipped across the frozen Tumen River into the North from China carrying a letter calling on North Korean leader Kim Jong Il to shut down the country's political prison camps. There has been no word from him since.

Park's parents last heard from their son Dec. 23 in an e-mail that predicted upheaval in North Korea.

"Know that I am the happiest in all my life," his e-mail read. "Incredible miracles are happening in the liberation of North Koreans right now ... We are going to see a big and beautiful change in Korea and in the World this year!"

Park was born in Los Angeles to Pyong and Helen Park, Korean immigrants who met in the United States. He spent much of his childhood in Tucson, Ariz., where he stayed after his parents moved to the San Diego area about four years ago.

His parents say he has devoted himself to church work since 2000, making regular Saturday runs to the slums of Nogales, Mexico, where he distributed food and did missionary work.

He planned to visit South Korea for about a month in June 2008 but ended up staying because he was deeply moved by the poverty of North Koreans, his mother said.

"He felt their pain so much," she said.

Park was in China, near the North Korean border, for about two months last summer to provide food and shelter to refugees, his parents said. He gave that up because he knew China would deport any refugees who got caught, exposing them to harsh punishment back home.

"He helped a lot of people," said Manchul Cho, an uncle. Neither Cho nor his parents knew how many refugees Park helped.

Back in Seoul, South Korea, Park worked with other organizations pressing for peaceful change in the communist nation. Pyong Park, 68, said his son wanted quicker results.

"He wanted to do a bigger thing," he said.

The Parks, who live in the north San Diego suburb of Encinitas, said they are in daily contact with the State Department. North Korea has not acknowledged Park is in the country.

"He was not afraid to die," Pyong Park said. "What he wanted was the whole world to know of North Korea's situation."

His only sibling, Paul, 38, also lives in the San Diego area.