Three North Koreans were shot dead by their own country's troops as they tried to cross the border into China, an activist in South Korea told a news agency Tuesday.
The men, who were in their 40s, were crossing the Yalu river near the city of Hyesan, Do Hee-Youn told the AFP news agency.
"People waiting at the Chinese side across the river to help the three defect saw the scene. The guards took with them the bodies which were lying on the ice," Do told AFP.
Do added that it was "very rare" for guards to open fire immediately on seeing people trying to flee and linked this to increased security following Kim Jung-il's death and the transfer of power to his son Kim Jong-un.
"I'm afraid it will become much harder for North Koreans to defect for a while," he told AFP."They are trying to let people know that those trying to flee will be shot dead right away."
AFP said about 23,000 North Koreans have fled repression or hunger since the 1950-1953 war with South Korea.
Earlier, South Korean President Lee Myung-bak called on Kim Jong-un to seize the opportunity and return to dialogue, saying he was prepared to offer help to revive the North's shattered economy if it suspends its nuclear activities.
"We have left the window of opportunity open," Lee said in a New Year address broadcast from South Korea's presidential Blue House. "If North Korea comes forward with sincerity, we will be able to open a new era for the Korean peninsula together.
"As soon as North Korea suspends nuclear activities in progress, six party talks should be able to resume. Through a six-party agreement, we are prepared to ease the North's security concern and provide necessary resources to revive its economy," he added.
Experts who study the North said it was unlikely it would take a dramatically different path under its new ruler, who at around 27 is believed to lack the experience or political support to initiate his own line of policy.
Reuters contributed to this report.