SEOUL (AFP) - North Korean troops shot dead three countrymen who were trying to cross the border into China, a Seoul activist said on Tuesday, as Pyongyang tightens border controls after the death of leader Kim Jong Il. Border guards last Saturday killed the men in their 40s who were crossing the Yalu river from the northern border city of Hyesan, said Do Hee Youn, who helps refugees from the North. '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,' Mr Do told AFP, citing sources in China's border county of Changbai. South Korea's intelligence service said it could not immediately confirm the reported shootings.