South Korea ? An American Christian missionary slipped into isolated North Korea on Christmas Day, shouting that he brought God’s love and carrying a letter urging leader Kim Jong Il to step down and free all political prisoners, an activist said.

Robert Park, 28, crossed a poorly guarded stretch of the frozen Tumen River that separates North Korea from China, according to a member of the Seoul-based group Pax Koreana, which promotes human rights in the North. The group plans to release footage of the crossing Sunday, he said.

“I am an American citizen. I brought God’s love. God loves you and God bless you,” Park reportedly said in fluent Korean as he crossed over Friday near the northeastern city of Hoeryong, according to the activist, citing two people who watched Park cross and filmed it. The activist spoke on condition of anonymity because of the sensitivity of the situation.

The State Department and the U.S. Embassy in Beijing said they were aware of the incident but had no details.